BURLINGTON, Vt., Feb. 21 -- Once Jalil Mirza decided to leave the United States to avoid possible deportation, nothing happened quite as he expected, not even goodbye.

As did hundreds of other Pakistanis fleeing a post-9/11 crackdown on illegal immigrants, Mr. Mirza quit his job, packed up his possessions and headed north rather than face a forced return to Pakistan.

After a 16-hour bus ride from Virginia with his wife and seven children, he arrived at the Canadian border, hoping to take advantage of Canada's political asylum law.

But besieged Canadian officials told him to come back in two weeks. And when he dragged their suitcases back to the American side, United States immigration agents promptly arrested him and his two teenage sons, leaving the rest of the family wailing in despair in the icy cold.

The Mirzas are part of an unusual and chaotic exodus that has jammed land crossings from the United States into Canada over the past two weeks, overwhelming immigration officials and refugee aid groups on both sides of the border.

It is an oddly reluctant migration toward a presumed safe haven by people who say they do not really want to go but feel compelled to for fear that they could be deported.

Prompted by rumors of dragnets and by new federal deadlines that require male foreign visitors, principally those from Muslim and Arab countries, to register with the government, families that lived illegally but undisturbed in the United States for years are now rushing to Canada. They get across the border only to be bounced back into the hands and jails of the Immigration and Naturalization Service.

Asylum applications to Canada have increased sharply since the beginning of the year, according to aid workers and officials on both sides of the border. Most of the applicants are Pakistanis, who are required to register with the American immigration service by March 21. Other nationality groups also face various registration deadlines, but have not noticeably flooded the border.

Many of the Pakistani asylum seekers said they decided to flee to Canada because they knew that Canada was already home to a large and growing population of Pakistani immigrants, especially in Montreal and Toronto.

Even before the latest upswing this month and last month, Pakistanis accounted for the largest number of asylum applications to Canada, according to Citizenship and Immigration Canada.

Refugee aid workers also speculated that the registration requirement hit Pakistani immigrants harder than other groups because more of them lived illegally in the United States and had less time to legalize their status through family ties or employment. A result is that hundreds of would-be refugees, some from as far away as Texas, are now camped out in Salvation Army shelters, mosques and other lodgings along the border, waiting for appointments to apply for asylum and struggling to find money to pay the bond to get their male relatives out of immigration detention.

Their common refrain, as was Mr. Mirza's, is that they love America and do not want to leave.

A former restaurant manager in Virginia with four young children born in the United States, Mr. Mirza, 45, managed to scrape together the $4,500 he needed to get himself and his older sons out of jail on bond. His family stayed two weeks in a shelter in Burlington, until today when they had an 8 a.m. appointment with Canadian immigration officials.

But Mr. Mirza wanted to show, one last time, that his heart was in the United States. "I'm going to turn and salute the American flag," he said as he approached the border. "I love America."

Even that plan, though, went awry. In the most prosaic of farewells, after filling out forms for eight hours he and his family were driven straight to the Canadian post at St. Bernard Lacolle, Quebec, early in the morning under a milky overcast sky. No one bothered to stop him on the American side, where the nearest flag hung limply on a pole in the distance.

"This is one of the most tragic events I've ever witnessed, seeing this exodus of good, hard-working families," said Patrick Giantonio, executive director of Vermont Refugee Assistance, which had found the shelter for the Mirzas and dozens of other Pakistani families trying to reach Canada.

"It's a tragedy not just for their communities," Mr. Giantonio added, "but for the American community."

Similar stories are playing out all along the northern border.

At crossing points in British Columbia, some 70 people, most of them Pakistanis, asked for asylum in January. In all of 2002, officials said, only 36 Pakistanis made refugee claims.

At land crossings into Ontario, 871 people applied for asylum in January, double the number just two months earlier. Last November, 5 percent of the asylum seekers were Pakistani. Last month, 49 percent were Pakistani, according to Canadian immigration officials in Toronto.

Freedom House, an immigrant aid group in Detroit, said that since the beginning of the year it had registered 269 Muslim asylum seekers trying to reach Canada in advance of their registration deadlines. Seven out of 10 are Pakistanis, with the rest Arabs. Normally, the group handles about 30 cases a month.

The surge of asylum seekers coincided with the start in December of a new registration program for men over the age of 15 who were in the United States on visitor, student or business visas. Within days, it became clear to foreigners that anyone registering who had overstayed a visa would be immediately put into deportation proceedings.

Although the registration law, dating to 1996, applies to all foreign visitors, the Department of Justice has put it into effect only for men from 25 countries, all but one of them Arab or Muslim nations. Of the 32,000 men who have registered so far at immigration offices around the country, according to officials, more than 3,000 face deportation.

The choices for illegal Muslim immigrants, then, were stark. If they had been in the United States for more than one year, they no longer had the right to apply for asylum here. So they could have ignored the registration and risked deportation, registered and faced deportation or gone back to Pakistan. Or they could try for asylum in Canada by claiming they would face political persecution if forced to return home.

They are not only overwhelming service agencies, but have also proved an embarrassment for the Pakistani government, which has been criticized at home for not demanding better treatment for its expatriates in exchange for its cooperation with the United States on fighting terrorism.

After the Pakistani foreign minister protested in Washington this month against the registration requirement, the deadline for Pakistanis was extended to March 21 from Feb. 21. The change also affected men from Saudi Arabia, who faced the same deadline.

But the extension is unlikely to stem the tide of people to the Canadian border, which has always registered shifts in immigration policy on either side with surges of people seeking asylum in Canada.

The widely held perception is that Canada treats applicants with more leniency, although its refugee approval rate of 57 percent is not much higher than that of the United States, which approves 54 percent of asylum cases. Asylum seekers in the United States are generally placed in detention while their claims are assessed, however, while those waiting for a decision in Canada are free to work.

Still, the latest tide of Muslim men and their families took authorities on both sides by surprise.

Three weeks ago, Canadian border officials at the crossings from northern New York and Vermont, said they did not have enough workers to handle the numbers of people asking for refugee status. They began giving applicants appointments for several weeks later and sending them back to the American side of the border.

In the past when unable to process people on the spot, Canada asked for assurances from the immigration service that those applicants would not be arrested after returning to the United States to wait for their interviews. But last month, Canadian authorities did not bother.

"We realized it was useless because whether or not we got assurances, we could not process these people," said Rene Mercier, a spokesman for Citizenship and Immigration Canada.

The United States, in turn, placed dozens of people in deportation proceedings even if they had documents showing an asylum appointment with Canada. Others, caught on their way to the border at counterterrorism checkpoints set up by the United States Customs Service, were arrested on immigration violations.

The arrests split families and left many women and children to fend for themselves at isolated border posts in some of the coldest weather in years. At least 50 people remain in detention along the border, unable to post bond.

The immigration service said its agents were simply following procedure. "Individuals who are illegally in the U.S. are processed the same way we would process them if we encountered them any other way," said Michael Gilhooly, a spokesman for the agency.

But it is a shock for those at the border. "I am crying, my wife is crying," said Samir Sheik, a Pakistani who had been working as a street vendor in New York City and was arrested at a checkpoint on his way to the Canadian border for having overstayed his visa. "It's not fair because I am leaving the country."

Mr. Sheik said that he could not return to Pakistan because he and his wife married against the wishes of both their families "a love marriage," as he tearfully described it and that he feared his wife would be killed by her father.

His wife, Erim Salim, shuffled silently around the crowded Salvation Army center in Burlington, where they had been reunited after she borrowed from friends and neighbors to pay his $5,000 bond.

"She is sick now, mentally," said Mr. Sheik, nodding toward her sadly. "Millions of people live here and are overstays. Why is it only for Pakistanis and Muslim people that they do this?"

Hiraj Zafer, a Pakistani cook from Salt Lake City who was also trying to enter Canada, gave an answer. "After 9/11, people hate us," Mr. Zafer said.

Mr. Sheik said: "Yes, they hate us. But we love America. We feel free here."