A little-noticed amendment in the closing days of Congress may shut off the flow of U.S. dues and other regular support to the United Nations, State Department officials said yesterday.

The diplomats, alarmed at the potential impact of the withdrawal of American financing from the world organization and several of its specialized agencies, sought to arrange an 11th-hour legislative rider to reverse the earlier action.

Chances for such a congressional reversal, as of last night, appeared slim. The sponsor of the original amendment, Sen. Jesse Helms (R.N.C.) informed of the possible sweeping effect of his legislative handiwork, said:

"Excuse me while I get my handkerchief out and wipe my eyes."

He said he would be pleased if U.N. funds are cut off, and a Helms staff aide said his boss would filibuster any effort to remedy the situation.

Sen. Ernest F. Hollings (D-S.C.), chairman of the appropriations subcommittee which handled the State Department money bill, said, "We'll see what we can do to be sensible about this" but added that any change in the law would have to wait until the next Congress in January.

The Helms amendment, adopted by voice vote Aug. 3, struck out $27 million in U.S. dues payments for international organizations and specified that no part of the U.S. dues money may be used for technical assistance by the U.N. or any of its specialized agencies.

The action did not raise much alarm at the time because the House has opposed this approach, and diplomats counted on the House-Senate conference committee to oppose the Helms amendment. The conferees followed expectations but, surprisingly, the full House at the urging of Rep. John H. Rousselot (R-Calif.) voted two weeks ago to back the Helms amendment and the Senate approach. One of the most conservative members of Congress, Rousselot is a former official of the John Birch Society.

At the State Department, the next development was the most disturbing: growing indications that the United Nations, under its finanical regulations, is unable to provide assurances that none of the U.S. dues money will be used for technical assistance.

For its part, the executive branch of government may not be able to disburse any of the estimated $200 million in regular assessments to the United Nations or its agencies without a legal assurance which the U.N. cannot provide. And according to State Department officials, top financial managers of the U.N. and its World Health Organization have said informally that the organizations cannot accept "restricted" funds in any case.

There has been a longstanding controversy over the appropriateness of using U.N. assessments - as opposed to voluntary contributions from various nations - for the purpose of technical assistance. Helms and Rousselot spoke to this question in pushing through the amendment. There was no mention in the debate that the action could imperil all U.S. dues money for the United Nations.

President Carter, apparently reluctant to veto the State Department appropriation bill at this late date, signed last Tuesday. But he did so protesting the Helms amendment, which he said "compromises this government's ability to fulfill its legally binding financial obligations to the United Nations and its specialized agencies." Carter said he intended to recommend "promptly" restoration of the technical assistance funds and elimination of the restrictive language which "jeopardizes our ability to support these international organization.