The Carter administration called yesterday for reorganizing the U.S. foreign aid program by putting most development assistance to Third World countries under the management of a new International Development Cooperation Administration.

If approved by Congress, the plan would consolidate in the new agency approximately $2.7 billion in nonmilitary aid programs now administered by the Agency for International Development and several other federal departments.

But, as described by administration officials, IDCA would be essentially a technical and monetary management agency without significant independent political power. In most matters where political considerations are involved in foreign aid, the ultimate decision -making authority still would rest with the State and Treasury Departments.

The proposal essentially is a truncated version of a reorganization plan that had been advocated strongly by outgoing AID Administrator John J. Gilligan and that was believe to have resulted in Gilligan's resignation two weeks ago under pressure from Secretary of State Cyrus R. Vance.

Gilligan had lobbied for a superagency with considerable independence from the State Department and with control over virtually all aspects of nonmilitary, direct and indirect foreign aid.

By contrast, the reorganization plan unveiled yesterday by Gilligan and Ambassador Henry Owen, a senior member of the National Security Council staff, described IDCA as "a small agency charged with coordinating, providing policy guidance and evaluating the development activities" of those agencies and programs that the administration proposes to put under its umbrella.

These include AID, which administers direct assistance to individual developing countries; the Overseas Private Investment Corporation, which insures and guarantees U.S. private investments in Third World nations, and the proposed new Institute for Technological Cooperation, which would support economic development research.

In addition, IDCA would share with Treasury the responsibility for recommending to the president those persons appointed as U.S. executive directors of multilateral lending institutions like the World Bank. It also would oversee management of U.S. budgetary contributions to international organizations such as the various development agencies of the United Nations.

However, the proposal fails to give IDCA control, as Gilligan had advocated, over the Peace Corps and the PL 480 Food for Peace program. Through its AID arm, though, it would continue to have a voice, along with the State and Agriculture Departments, in administering PL 480 assistance.

In response to questions, Gilligan and Owen conceded that authority for two major aspects of foreign aid -- financing of U.S. contributions to the multilateral banks, which currently are the principal conduits for U.S. financial assistance, and decisions on when to grant or withhold aid for political policy reasons such as human rights -- would remain with Treasury and State respectively.

State also would continue to decide which countries get Security Supporting Assistance, a form of aid currently involving approximately $2 billion and that channels money for nonmilitary purposes to financially hard-pressed strategic allies of the United States. However, once these SSA requests are approved by Congress, IDCA would be responsible for administering them through AID.

In describing the plan, administration officials characterized it as the "first far reaching reorganization" of foreign aid activities since AID was created in 1961. They also called it a major step in Carter's program for extensive reorganization of the federal government to make it more efficient, responsive and accountable to Congress and the public.

In its main outlines, the proposal closely parallels a reorganization bill introduced in Congress last year by the late Sen. Hubert H. Humphrey (D-Minn.).Although the Humphrey bill has been sidetracked, its aims have considerable support in both houses of Congress.

Although Carter has not yet named a successor to Gilligan, the head of the new agency is expected to be Thomas Ehrlich, currently head of the Legal Services Corp., a federally funded independent organization that provides legal aid to the poor.

Under the proposed reorganization, the IDCA director would be designated formally as "principal development adviser" to the president and secretary of state. The agency, which now is under the control of State for all practical purposes, would achieve a greater degree of semi-independence such as that enjoyed by the Arms Control and Disarmament Agency.