The Senate broke through another wall of resistance and began actual work on extension of the Voting Rights Act of 1965 yesterday, handily defeating a series of weakening amendments as Majority Leader Howard H. Baker Jr. (R-Tenn.) took debate into the early morning in a futile effort to pass the bill.

"It's just a question of whether we can slog our way through," he had told reporters earlier yesterday. Final passage is expected today, he said.

The Senate voted, 97-to-0, to take up the measure, ending six days of filibustering by a small group of conservatives led by Sen. Jesse Helms (R-N.C.).

Helms, who was under pressure from fellow Republicans to allow work to begin on the measure and was apparently mollified by promises to take up some of his pet projects later, abandoned his threat to bring abortion rights and school prayer into the debate.

By votes of 81 to 16 and 81 to 14, senators rebuffed efforts by Sen. John P. East (R-N.C.) to roll back one of the bill's most controversial sections. It prohibits officials from using any voting procedure resulting in racial discrimination.

East argued that the section would require racially proportional representation in every election district and wanted it rewritten to require proof of intent to discriminate as grounds for legal action.

The Senate refused, insisting that the bill's new language rules out proportional representation, and then agreed to defeat, at Helms' request, a paradoxical Helms amendment that would have required proportional representation. That vote was 94 to 1.

The conservative group argued that the voting rights bill is less an extension of the 1965 act than a thorough rewrite aimed at punishing their states.

They contested the contention by Democratic leaders that the rewrite would make it easier for the affected parts of 22 states to escape the act's provisions, which have effectively required since 1965 that the Justice Department approve all changes in voting laws in those areas.

But supporters of the measure agreed with the Leadership Conference on Civil Rights that continued clearance of new voting laws is "designed to prevent backsliding" in areas with long records of racial discrimination.

The Senate then turned back two East amendments--voting 65 to 31 against one that would have opened bailout efforts to courts other than the U.S. District Court here, and 78 to 19 against one that would have shortened the life of the extension.

Changes permitting quicker settlement of bailout suits and clarifying bilingual aid requirements for speakers of nonwritten languages passed on a voice vote.

The House passed the extension last year and said no conference would be needed to send the unamended Senate version directly to the president.

In a novel development, most of the Senate's substantive debate took place during the six days of filibuster that preceded yesterday's action.

Trying to pressure his colleagues into concessions, Helms said in an open letter, released yesterday and headed "Dear pro-life friend," that he was planning to try attaching his anti-abortion bill to the Voting Rights Act as an amendment.

Anti-abortion groups immediately rallied, circulating letters of support for the move and for another possible Helms amendment to restore prayer in public schools. But as Sen. Robert J. Dole (R-Kan.) later explained, "a number of rather restless Republicans made it clear" to Helms that they wanted to proceed with the extension without debate on abortion.

Hatch, who insisted he has always favored an early vote despite his prolonged speeches during the filibuster, said Helms had been advised that anti-abortion amendments "would be better considered at another point."

Baker denied that any deal had been struck to get Helms to back off from his threat and his filibuster but added he had "mentioned several times" that work on Helms' pet constitutional amendment to require a balanced federal budget would have to await passage of the voting rights act extension.