An American official said yesterday that the Reagan adminisration, facing an expanded Arab drive to expel Israel from U.N. agencies, is prepared to "withdraw official U.S. participation in and cut off funding for" any international body that bars Israeli delegates.

This stance, said a State Department official, follows "the clear-cut mandate of the Congress and the equally clear-cut will of the president" and represents no change in administration policy. But it is the first time the consequences of such a U.N. action -- before described publicly only as "dire" -- have been spelled out in specific terms.

The consequences for the institutions involved could be serious since the United States provides a quarter or more of the budgets for the United Nations and its agencies.

The American officials made clear that the policy would be applied to the International Atomic Energy Agency, which on Sept. 24 voted 41 to 39 to reject the credentials of the Israeli delegation. It is currently the only agency excluding Israel.

At the time of the vote in Vienna, the State Department announced that it was "reassessing" American participation in the agency. The United States has not acted to cut its links with the IAEA, and Gordon Streeb, deputy assistant secretary of state for international and development affairs, said that "I know of no such decision."

But he said that U.S. participation in IAEA meetings in Vienna has been halted, with U.S. diplomats attending only as observers, and the United States has acted to cancel an IAEA seminar scheduled in Texas and to end the funding of new fellowships through the agency.

During the past week, the anti-Israel drive has expanded to other U.N. agencies. Algeria has submitted a resolution at a conference of the 157-nation International Telecommunication Union in Nairobi, Kenya, calling for Israeli expulsion from the agency for its role in the Beirut massacre.

U.S. officials say they have received indications that a similar move will be made at a Geneva meeting of the executive committee of the Office of the U.N. High Commissioner for Refugees, scheduled to open Oct. 15.

Congress already has indicated its support for punitive action against agencies that constrict Israeli participation. Resolutions supporting an American walkout and dues cutoff in such instances were adopted this spring by a unanimous vote in the Senate and a vote of 401 to 3 in the House.