Hispanic activists said yesterday they fear social service agencies won't be able to handle the onslaught of new clients that are expected because of two federal actions giving temporary legal status to thousands of Salvadoran and Guatemalan immigrants in this area.

On Wednesday, the federal government agreed to give temporary legal status to an estimated 500,000 undocumented Salvadoran and Guatemalan immigrants nationwide who since 1980 have applied for political asylum but were rejected.

That agreement, part of the settlement of a long-standing court case, is expected to be finalized on Dec. 31. Two days later, the Immigration and Naturalization Service will begin a congressionally mandated program that gives temporary legal status for 18 months to all undocumented Salvadorans in this country.

That program is expected to affect 300,000 people. Some Salvadorans would benefit from both programs, which would provide work authorization and could ultimately lead to U.S. citizenship.

In the Washington area, as many as 50,000 people could be affected, said Susana Cepeda, executive director of the District's Council of Hispanic Agencies.

Agencies that provide legal services for Spanish-speaking clients plan to help them fill out the applications they will need to qualify for the temporary legal status.

Already, the agencies have been lobbying hard with the INS to simplify the process. But agency officials say the INS program is still too complex, involving multiple visits, which might discourage applicants.

"I'm concerned about how agencies are going to deal with people who come knocking on their door, when the agencies' resources are depleted," said Cepeda, whose agency provides technical assistance to community agencies that serve District Hispanics.

Duke Austin, an INS spokesman, said the immigration service will rely heavily on community agencies to help it process the applications.

While details of the court settlement have not been worked out, Salvadorans affected by the new law have 180 days to apply for temporary protective status. "We'll accommodate them in that period of time," Austin said.

But in meetings this week between immigration officials and community services agencies, both sides expressed concerns about handling the workload in the six-month time period Congress mandated in October when it passed the law granting temporary legal status.

"It will cause us some problems in areas," Austin said.

"Unfortunately, resources for all social agencies are diminishing," said Lael Parish, executive director of CASA de Maryland, a community agency in Takoma Park. "Times are hard and getting harder, particularly for those of us who deal with the Central American community."

Clare Cherkasky, director of immigration services for Hogar Hispano, an Arlington agency, said the workload for her organization, which sees 150 clients a day, is likely to double in the coming months.

She estimated that the new ruling will affect half of the Salvadorans in the region. Most Salvadorans in the area arrived here after 1982 and did not qualify for citizenship under an amnesty provision in a 1986 immigration law.

The immigration program that begins on Jan. 2 will give all Salvadorans who entered this country illegally before Sept. 19, 1990, the opportunity to have their immigration status changed for 18 months, if they can prove that they have not left the United States since they entered -- or that they have not been convicted of either two misdemeanors or one felony.

"Successful applicants will receive work authorization, to be renewed every six months," said Daniel A. Katz, executive director of the Central American Refugees Center, based in Washington.

At the end of 18 months, the immigration service will begin deportation proceedings against anyone who doesn't qualify to remain in the United States, Katz said.

The court settlement reached in San Francisco provides temporary legal status to all Salvadorans and Guatemalans denied political asylum since 1980, and gives them a new asylum hearing.

Sandra Campos, 23, a native of the Salvadoran city of San Miguel, said she was jubilant when she learned of the impending change in policy. Campos said she came to the area a year ago, and applied for asylum, but decided not to go to the immigration hearing on her case.

"I was afraid of being deported," she said.