BROWNSVILLE, Texas (AP) _ A judge on Monday blocked a new government immigration policy blamed for forcing hundreds of homeless Central Americans in south Texas to live in primitive camps and condemned buildings.

U.S. District Judge Filemon Vela's temporary restraining order restores a previous Immigration and Naturalization Service policy that allows asylum seekers in south Texas to travel to other U.S. destinations after checking in with the INS.

Hundreds of the asylum-seekers have camped out in Cameron County, Texas' southernmost county, since the INS adopted a policy Dec. 16 that all but prevented them from leaving the area while their applications for political asylum were processed.

''One would have to be blind not to recognize that we have a problem,'' Vela said, in putting the INS policy on hold.

The temporary restraining order was sought in a lawsuit filed against the INS on Friday by refugee advocates.

''Everybody is euphoric about the good news,'' said Vidal Sanchez, 38, of Nicaragua, who has lived for more than two weeks in a primitive camp near Brownsville with more than 300 other Central Americans awaiting appointments with the INS.

Sanchez said he planned to leave for Miami by Wednesday.

He and other campers, many staying under tents fashioned from tree limbs and discarded sheets of plastic, were told Sunday they would have to vacate the land after the property owner posted ''No Trespassing'' signs.

The campsite's population continued to drop Monday as the immigrants complied with a sheriff's order to leave or face trespassing charges. The aliens have been offered shelter in several nearby churches.

By late Monday, only about 50 Central Americans were living in the camp, and many said they did not plan to spend the night.

The shantytown is across the street from the Catholic Church-operated Casa Oscar Romero shelter for Central Americans, which for months has been filled to its court-ordered maximum occupancy of 200.

U.S. Rep. Solomon Ortiz, D-Texas, announced Monday that he had obtained assurances of immediate federal assistance for Cameron County in providing food and shelter for the influx of Central Americans.

Ortiz said he and a team from the Justice Department's community relations service would tour the county and make recommendations for immediate action.

Ortiz said the ideal situation would be to make use of existing space in federal buildings.

Vela's temporary restraining order will be in effect until Thursday, when the judge scheduled a hearing to decide whether to issue an indefinite preliminary injunction against the new INS procedure.

Vern Jervis, an INS spokesman in Washington, said the agency will contest the restraining order.

The INS policy, which applies to any district where aliens apply for asylum, was defended Monday by attorney David Ayala.

''Your honor, the immigration service is not to blame for the plight of the people who are out there,'' Ayala told the judge.

Jervis said the new procedure was designed to curb abuses of the asylum process that created backlogs of thousands of cases in some cities. More than 30,000 asylum-seekers passed through the INS Harlingen District at the southern tip of Texas last year.

Most asylum applicants do not qualify for refugee status, Jervis said, because they are here for economic, not political reasons.

Under the Dec. 16 policy, INS officials were telling applicants they could not travel from the area or work while awaiting a decision on their asylum status, a period of at least 30 days.

After Vela's order, the victorious immigration attorneys went to tell the aliens of their changed status.

''We're going to advise people that they do not have to live here in the (Rio Grande) valley in the rain and the cold and vacant lots, that they can now be with their family, with their friends and they can pursue their asylum claims in those (destination) cities,'' said Mark Schneider, an attorney with Proyecto Libertad, a co-counsel to the lawsuit.

''It's marvelous,'' said Maria Isabel Fernandez, 28, of Honduras, who has camped for two weeks near Casa Romero. ''What else could we ask for?''

She and eight relatives said they planned to travel to Houston, where they have family.

Sister Juliana Garcia, director of Casa Romero, said many people at the shelter started preparing to travel as soon as they heard about the court order.

''I think it will alleviate the situation for a lot of people,'' Sister Juliana said. ''People are already making a big line to fix their papers and leave.''

The lawsuit against INS Commissioner Alan Nelson and U.S. Attorney General Richard Thornburgh was filed by Brownsville immigration attorney Linda Reyna Yanez, Robert Rubin of the San Francisco Lawyers' Committee for Urban Affairs and the Harlingen-based Proyecto Libertad immigrant legal advocacy office.

It accuses the INS of implementing a policy change without publishing it in the Federal Register for public comment, and of depriving asylum-seekers of their rights to representation and access to the asylum process as required by U.S. law under the Refugee Act of 1980.