Senate and House foreign affairs conferees agreed yesterday to authorize resumption of full financing of the U.S. share of the United Nations budget but the compromise gives Congress the right to withhold a small portion of appropriated funds if the world body falters on its promised budgetary reforms.

All restrictions on funding would be lifted after two years if the United Nations lives up to its commitments on these reforms, according to congressional sources. Congress is not expected to appropriate enough money to bring the United States current on its outstanding dues -- which at one point this fall reached $414 million.

The compromise cleared the way for passage of a two-year, $8.3 billion State Department authorization bill stripped of most of the heavily criticized Senate amendments that sought to influence U.S. foreign relations. Sen. John C. Danforth (R-Mo.) had charged that the Senate Foreign Relations Committee was creating "a cacaphony of confusion" about U.S. foreign policy.

The committee has been stung by those remarks as well as criticism of its general performance under Chairman Claiborne Pell (D-R.I.) and the ranking minority member, Jesse Helms (R-N.C.), who are widely apart politically.

Aides to Pell and Helms said agreement on the Senate bill and the conference report showed the two senators were capable of working together and had resolved 170 items of conflict.

Senate conferees agreed to remove provisions that would have forced the State Department to create a number of new high-level posts and cancel two U.S.-Soviet agreements on the building of new embassies in their respective capitals.

The complicated compromise reached over the contentious issue of U.S. funding of the United Nations effectively voids the amendment, passed two years ago, that reduced the U.S. share of the U.N. budget from 25 percent to 20 percent until the world body carried out reforms giving the main financial donors more decision-making power.

At one point this fall, the United States was $414 million in arrears on its dues, including the $212 million it was supposed to contribute to the 1987 regular budget. Part of the arrearage was caused by the amendment and part was caused by general U.S. budgetary constraints. But in the past few weeks, the administration has paid $100 million of its assessed 1987 dues.

The State Department withheld comment on the Senate-House compromise. One official said that although the department had not seen the text, the administration does not think Congress will appropriate all the funds that have been authorized.

"We owe X amount of dollars, and Congress is not giving us the dollars," the official said. "We'll have some more money but the question is how much will we get?"

The conference report would have the United States pay 40 percent of its U.N. dues on Oct. 1, the start of the U.S. fiscal year. Another 40 percent will be paid once the president reports to Congress that the United Nations is proceeding to implement a reform that requires budgetary decisions to be made on a consensus basis rather than the past one-nation, one-vote principle.

The final 20 percent would be paid 30 days later unless Congress, after hearing the president's report, passed a joint resolution prohibiting the payment. Even if Congress appropriated less than the full amount of U.S. asessed dues -- as seems likely this year -- the last 20 percent of the appropriation would be subject to the provision.

The president also would have to report progress on reducing to 50 percent the number of employes working on loan at the U.N. Secretariat. The measure is aimed at forcing the Soviet Union to stop the practice of placing KBG agents on a temporary basis there.