With the historic vote set for this evening, supporters and opponents of the proposed constitutional amendment to give the District of Columbia voting representatives in Congress agreed yesterday that the century-old dream of city residents is within a couple of votes of the two-thirds majority needed for passage in the Senate.

Four previously undecided senators added their support to the measure yesterday as proponents, led by Sen. Edward M. Kennedy (D-Mass.), defeated five weakening amendments during 6 1/2 hours of debate.

A Washington Post survey of all senators yesterday showed 57 votes for the proposed amendment, three more senators leaning toward voting in favor, 24 against and 16 senators undecided.

Dick Clark, of Common Cause, who heads the ad hoc Self-Determination for D.C. lobbying group, studied the list of members in the Senate lounge last night and counted "60 hard votes" in favor. Other estimates by supporters went as high as the 65 tallied by Del. Walter E. Fauntroy, the city's nonvoting representative in the House. With 99 senators expected to be present tonight (Sen. James A. Eastland is out of the country), 66 votes would be required for the two-thirds majority.

Frantic 11th hour maneuvering by supports included the assembling of a who's who of the civil rights movement in the Senate gallery for today's vote scheduled for 6 p.m., and a personal telephone campaign yesterday and again today by Vice President Mondale to undecided Democrats.

Kennedy, floor manager of the bill, said last night that "it will be decided by one or two votes." His opposite number, Sen. William L. Scott (R-Va.), agreed, saying "it's a winnable situation" for opponents, but "I can't say that with a high degree of confidence. There are a number of doubtfuls."

The new supporters of the bill yesterday were Sen. Jennings Randolph (D-W.Va.), Richard Lugar (R-Ind.), Lloyd M. Bentsen (D-Tex.) and John H. Chafee (R-R.I.). One previously undecided senator, William V. Roth Jr. (R-Del.), said he would vote against it.

If it wins approval in the Senate today, the resolution must be approved by the legislatures of 38 states within seven years before it can take effect. The legislation passed the House by overwhelming majority last spring.

The most serious challenge to the House-passed language yesterday came on an amendment offered by Sen. James A. McClure (R-Idaho) that would have retroceded to Maryland the inhabited portions of the city. That amendment was tabled, or in effect killed, by a vote of 57 to 35. It was the only one of five recorded votes on which supporters of D.C. voting representations could not under a two-thirds vote.

Debate on McClure's amendment produced the sharpest exchange of the day. Attempting to counter suggestions that some opposition to the proposed constitutional amendment results from racism, McClure said. "If there is racism, it lies in the political structure of the state of Maryland" for opposing retrocession.

That charge brought Sen. Paul S. Sarbanes (D-Md.) out of his seat angrily shouting that McClure had "no basis" for "casting (such) aspersions." Sarbanes said he and his Maryland colleague, Republican Charles McC. Mathias, "didn't ascribe those motives" to McClure for his opposition to the main idea.

Sarbane and Mathias both support voting representation for D.C., while both senators in neighboring Virginia, Republican Scott and independent Harry F. Byrd Jr., oppose it. Scott is floor leader of the opposition.

The outburst was one of the few time during yesterday's debate that any of the so-called "four toos" that some supporters contend lies behind opposition to the measure - that any senators and House members elected by the majority-black voters of Washington would be "too black, too liberal, too urban and too Democratic" - surfaced.

Also turned back were amendments by apponents that would grant statehood to the city, tabled by a vote of 67-to 17: prohibit any state legislature from recinding its ratification, tabled 67 to 5; set up a mechanism for filling vacancies in the District's congressional delegation, tabled 50 to 28; all offered by McClure, and a Scott proposal that would tack on an unrelated constitutional amendment that would permit the abortion issue to be decided by the various states, tabled 49 to 18.

Another opponent, Sen. Orrin G. Hatch (R-Utah), recited a list of oversight functions Congress has imposed on the District's elected officials.

Sen. Jesse A. Helms (R-N.C.) accused supporters of the proposal of engaging in "a mad scramble for political advantage with a minority group." He said the Senate was "participating in a charade" because "there is not one senator who believes it will be ratified."

Helms said the House-passed measure had bypassed a vote by a Senate committee and was "virtually bludgeoned onto the Senate calendar" by a list of supporters "loaded with presidential candidates seeking black votes."

"Blacks should not be deluded." Helms continued, predicting that the ratification battle over the D.C. issue "will make the ERA extension fight look like a cakewalk. You can bet your boots there will be an effort to extend the deadline," he went on.

Kennedy answered that, unlike the Equal Rights Amendment, the D.C. proposition specifically limits the ratification period to seven years as part of the main language of the resolution.

Kennedy also said last night that if the measure gets to the ratification stage he is "hopeful people will realize the fundamental issue of justice and that will carry it" into law.

President Carter, who has consistently supported the resolution as it weaved through the legislative process, issued another statement yesterday in which he said, "I strongly urge the Senate to pass the resolution."

Among factors named by Carter was the fact, cited over the weekend by Majority Leader Robert C. Byrd (D-W.Va.) in announcing his support, that "District residents have fought and died in every war since the War for Independence. During the Vietnam conflict, only three states suffered greater casualties than the District."