Two Prince George's County social workers, a Maryland prison guard, and a former guard have been arrested by Immigration and Naturalization Service agents and charged with being illegal aliens.

The guards, who are from Nigeria, worked at the Maryland House of Corrections in Jessup and the social workers, who are from Sierra Leone, were employed by the State Department of Social Services. All four of the Africans face deportation proceedings, according to a spokesman for the federal agency.

"We arrest about 150 people a month for being illegal aliens but they're usually not state employes making $15,000 to $20,000 a year," said Tom Graber, a investigator in the immigration service's Baltimore office.

Spokesmen for the state agencies that employed the four said yesterday they did not know if officials had asked them if they were American citizens when they were hired.

State personnel director Theodore E. Thornton Sr. said the arrests, which occurred over the last two days, may indicate that there is a loophole in the state's hiring system. He said that his office "will take appropriate corrective action."

All four came to the U.S. as students and remained in the country after their visas expired, according to Jesse Grogg, an immigration official.

The social workers were identified as Sonah Kamara and Isabella Violet Max-Johnson. Grogg refused to disclose any further information about the two women, saying that his investigation was incomplete.

Department of Correction spokesman Beverly Marable said that one arrested guard, Wellington Obichere, had been employed for eight months and the former guard, Babatunde Adenowo, had worked for five months. Both were arrrested at their homes in Baltimore.

Adenowo was fired Jan. 7, Marable said, because "on numerous occasions he didn't report to work." Obichere was fired yesterday because of his alleged illegal alien status, she said.