Maneuvering for the last few votes needed to assure success, Senate proponents of the balanced-budget amendment yesterday said they have agreed to accept some changes even though this could complicate final passage in Congress this year.

Both sides in the debate have indicated they expect a cliff-hanging vote later this week with the outcome probably turning on the decisions of four or five senators.

The constitutional amendment aimed at forcing Congress to pass balanced budgets requires 67 affirmative votes in the Senate and Sen. Orrin G. Hatch (R-Utah) said proponents can count on 63 certain and two probable votes, with four more that could surface in the final hours.

Hatch said three amendments offered by Sens. Pete V. Domenici (R-N.M.) and Lawton Chiles (D-Fla.) are acceptable to him, despite his earlier statements that all amendments would be opposed. He explained that allowing those changes would bring Chiles "on board" as a supporter.

Hatch acknowledged that any changes in the language "increased the risk" that the measure may fail because if it gets to the House floor under the planned discharge petition amendments would be difficult to attach. That would mean substantially different versions would have to be reconciled in a House-Senate conference, a process proponents want to avoid.

Opponents of the proposed constitutional amendment said they have decided not to filibuster but have planned a series of amendments that will require extended debate. One of them would exempt Social Security and veterans benefits from the balanced-budget requirement.

Sen. Alan Cranston (D-Calif.), a leader of the opponents, has estimated that 63 senators favor the original amendment with 31 opposed, leaving six undecided.

The proposed amendment would require Congress to pass budgets in which outlays do not exceed receipts, unless both houses vote to do so by three-fifths votes or unless the country is at war.

Budget Director David A. Stockman is urging one change which would lift the budget-balancing requirement in the event a national emergency, not a war, is declared, Hatch said. He said his forces object to that change.

One of the Domenici-Chiles amendments which Hatch has accepted would prohibit the president from using the measure to impound funds or exercise a line item veto over the contents of spending bills. Critics have contended that a power-seeking president could exploit the present language to expand his ability to alter congresional budgets.

Another change could make it clear that Congress, if the amendment is ratified by the states, would have authority to pass implementing legislation that would spell out how the measure is to be enforced. Some have claimed there is no way legally to force compliance on Congress.

A third change would provide more flexibility for Congress to establish a formula for arriving at an estimate of national income. The amendment specifies that the government cannot increase tax receipts by a rate greater than the increase in national income.

Meanwhile, it was learned that the Senate Judiciary Committee had dropped from the amendment it sent to the floor a section that would prohibit the federal government from assigning new responsibilities to states without their consent unless it also provided funding.

Several supporters of the amendment as well as opponents were not aware this change had been made. The National Tax Limitation Committee has continued to distribute literature that includes the deleted section, as does the Judiciary Committee report on the legislation, even though the text sent to the floor does not.

The text of the amendment carried in Sunday editions of The Washington Post included the provision and a story referred to it. Some amendment opponents may make an issue of the dropped provision, which was intended to prevent balancing of the federal budget by giving programs to the states.