Federal law enforcement authorities, unsuccessful at laying their hands on fugitive ex-CIA employe and arms dealer Francis E. Terpil, have asked a judge to let them sell Terpil's $260,000 McLean home to help satisfy a tax bill totaling $4.6 million.

Terpil and his wife, Marillyn, fled the country sometime after Terpil and ex-CIA agent Edwin P. Wilson were indicted in April 1980 in the District on charges of murder conspiracy and illegal arms and explosives sales to Libya.

The Justice Department, in a complaint filed this week in U.S. District Court in Alexandria, said the Terpils owe federal income taxes for 1977 and 1978 totaling about $3.6 million, plus an additional $1 million in penalties and interest.

Reportedly known to his suburban Virginia neighbors as a friendly but quiet importer-exporter who was frequently away from home, Terpil allegedly profited from multimillion dollar arms deals with Libya and Uganda.

Federal officials declined to say yesterday whether Terpil's sizeable tax bill was related to the allegedly illegal overseas deals.

An affidavit filed by Justice tax lawyer Michael J. Kearns said Terpil, who once bragged about selling torture devices to Uganda's Idi Amin, was known to be in Beirut, Lebanon, last November. Kearns would not say yesterday how authorities knew that.

"We've got lots of people telling us where Frank is," said another Justice lawyer familiar with the Terpil investigation.

Marillyn Terpil, who also faces a federal conspiracy charge in New York for allegedly helping a former Iranian official obtain a U.S. passport illegally, surrendered a month ago to U.S. authorities in New York and is free on bond.

Assistant U.S. Attorney Raymond Levites in New York said yesterday that Marillyn Terpil returned to the United States under an arrangement negotiated by her lawyer and a U.S. Customs agent at the American Embassy in London.

Federal officials declined to say whether she had been living abroad with her husband. Under conditions of her bond, Marillyn Terpil has been allowed to visit recently with her parents in Warrenton, Va., about 50 miles west of the District, said officials familiar with the case.

The Japanese-style Terpil home at 1102 Chain Bridge Road has been vacant since the couple left the country. Justice lawyer Kearns said yesterday he believed the house had fallen into disrepair and had been extensively vandalized.