A federal appeals court, in a ruling that could affect thousands of immigrant families, overturned a Bush administration regulation Tuesday and said children who were allowed to join their families in the United States while they sought visas could remain past age 21.

The ruling by the Ninth U.S. Circuit Court of Appeals in San Francisco affects families in which one or both parents had become legal U.S. residents and applied for the same status for their children living abroad.

Congress passed a law in 2000 saying children who had been waiting outside the United States at least three years for their permanent visas to be approved -- half the average waiting period -- were eligible for a temporary visa called a V-2 that would let them enter the country, hold a job and await the outcome of their applications. The law applied only to children whose parents had already applied for visas for them by December 2000.

The law said children under 21 were eligible for V-2 visas but was silent about whether they could keep the visas once they turned 21. A federal regulation, issued in April 2001 by the Immigration and Naturalization Service, revoked V-2 visas at 21 and required their holders to move outside the United States to resume their wait for permanent status.

The ruling resulted from a Southern California case of two Filipinos who entered with V-2 visas shortly before turning 21 and were ordered to leave almost immediately. The appeals court said the 2001 regulation was contrary to the clear purpose of the 2000 law: "to reunite families of immigrants petitioning for permanent residency until the petitioner's visa number comes up.''

Judge James Browning said in the 3-0 ruling that congressional sponsors of the law expressed the intent to let children live with their families while awaiting permanent visas and never indicated that turning 21 would disqualify them.

The ruling, which applies to California and eight other Western states under the court's jurisdiction, would affect tens of thousands of families if applied nationally, said Robert Reeves, an attorney for the immigrants in the case.

Calling the INS regulation a typically "mean-spirited and heavy-handed application ... of the laws Congress passes,'' he said something should also be done for children who had been forced to leave the country.

There was no immediate comment from U.S. Citizenship and Immigration Services, the successor to the INS.

E-mail Bob Egelko at begelko@sfchronicle.com.