An arm of the American Civil Liberties Union called yesterday for Congress to probe charges that the Central Intelligence Agency conducted illegal operations inside the United States in an effort to influence U.S. policy in Central America.

The Center for National Security Studies said a probe by House and Senate intelligence committees should focus on published interviews with Edgar Chamorro, an official of the Nicaraguan Democratic Front (FDN), the largest of several U.S.-backed groups of rebels fighting the leftist government of Nicaragua.

Chamorro told The Washington Post and The New York Times that the CIA had instructed FDN leaders to misrepresent their policies in talking to members of Congress, in order to induce Congress to keep funding the rebel effort.

CIA officers arranged flights to Washington for the rebels, briefed them on members of Congress and advised them on the best lobbying approaches, Chamorro said in the interviews.

"If these reports are true, the administration's covert operation against Nicaragua . . . has resulted in an egregious covert interference with our domestic political process," center director Morton H. Halperin said in letters to the committees.

Sen. Daniel Patrick Moynihan (D-N.Y.), vice chairman of the Senate intelligence committee, wrote CIA Director William J. Casey last Friday asking whether Chamorro's charges are true and, if so, which members of Congress were targeted for lobbying.

A spokesman for the House Foreign Affairs Committee said yesterday that the issue would be included in hearings set for the first week in December on a CIA manual that advised the Nicaraguan rebels on "selective use of violence" to "neutralize" political targets.