A House-Senate conference committee reluctantly agreed to cuts in the $3.9 billion U.S. share of financing for two international regional-development banks in an attempt to gain House approval of the measure.

Sen. Frank Church (D-Idaho), chairman of the Senate Foreign Relations Committee, said everyone in the room "would live to regret" the decision to go along with the cut.

Rep. John J. Cavanaugh (D-Neb.), another member of the conference committee, said he and a collaegue spent two hours with Treasury Secretary G. William Miller yesterday morning in a vain effort to persuade him to reverse the administration's decision to go along with the cut.

"This represents a critical absence of political will" on the part of President Carter, Cavanaugh declared. "Never again can a president negotiate" U.S. contributions to such international financial organizations as the regional-development banks, the International Monetary Fund and the World Bank "with the confidence he can fulfill the commitments he negotiates" the congressman warned.

At stake in the conference were a negotiated commitment of $3.45 billion to the Inter-American Development Bank and $445 million to the Asian Development Fund. Earlier, the House had cut these sharply, and when a conference committee issued a report restoring the cuts, the House refused to accept it.

Yesterday's action cuts the IADB back to $3.1 billion, a 10 percent reduction. Money for the Asian bank was trimmed 15 percent to $378 million.

The House hadn't reduced the $125 million commitment to the African bank, and it remained unchanged in the conference agreement.

Cavanaugh, who refused to sign the conference report, said Miller felt the administration didn't have enough votes to reverse the outcome of April 17 when the House rejected the last conference report by a vote of 211 to 180. 1

Part of the regional-development banks opposition, led by conservative Republicans, has focused on the cost of such aid at a time of tight budgets.