A federal judge's ruling in south Texas opened the way Friday for the Immigration and Naturalization Service to erect a tent city near the Mexican border and detain Central American refugees.

Judge Filemon Vela said he would allow the INS to restrict the travel of refugees beginning noon Monday.

Robert Rubin, a lawyer for the refugees, immediately announced an appeal of the judge's ruling.

Since Jan. 9, when the judge's order blocked the use of INS travel restrictions, about 10,000 Central Americans seeking political asylum streamed through South Texas, according to the INS. Some 40 percent were Nicaraguans, most of whom were bound for Miami.

Despite Friday's favorable ruling, INS spokesman Duke Austin said the agency would take no action until it presents to the judge its plans for dealing with the refugee influx. Because of the Monday holiday for Washington's birthday, that may not happen until Tuesday.

Congressional sources have said the agency intends to set up a fenceless tent city for the refugees on government land near Port Isabel, Texas. A White House spokesman said Friday that no final decision has been made on the plan.

Refugee attorney Rubin said he was heartened that the judge expressed strong displeasure with the government's handling of the refugee problem, and called the legal issue in the case "a close one."

The INS had first imposed travel restrictions in December, forcing hundreds of refugees onto the streets of South Texas communities while they awaited a decision on their political asylum claims.

Before then, the Justice Department had encouraged Nicaraguan refugees to apply for political asylum. Once across the border, the refugees were allowed to transfer their cases to other cities and were issued work permits.

The result was a wave of Nicaraguan migration to Miami, forcing the city at one point to house refugees in a baseball stadium.

The INS contends that many Nicaraguans are taking advantage of the political asylum process by filing frivolous applications. According to the INS, most of the Nicaraguans are fleeing economic collapse, not political oppression.

But Rubin said that INS figures belie that claim. In fiscal year 1988, the approval rate for asylum petitions from Nicaraguans was 53 percent.

In his six-page ruling, Vela castigated the government for creating the South Texas bottleneck in the first place.