The Senate Judiciary Committee yesterday approved a bipartisan compromise bill to extend and strengthen key provisions of the 1965 Voting Rights Act, defeating a series of weakening amendments.

The compromise, supported by more than 70 members of the House as well as the Reagan administration and civil rights groups, was worked out by Sens. Robert J. Dole (R-Kan.), Edward M. Kennedy (D-Mass.) and Charles McC. Mathias (R-Md.) and announced on Monday. Key provisions of the act had been scheduled to expire in August.

The committee voted, 14 to 4, to accept the compromise. Opposing the measure were Republicans Strom Thurmond of South Carolina, who chairs the Judiciary Committee; Orrin G. Hatch of Utah; Jeremiah Denton of Alabama, and John P. East of North Carolina.

East said he believed the proposal would cause as much disruption to the U.S. political system as busing for desegregation has caused in public education.

At issue in the voting rights fight has been the standard of proof to apply in proving racial discrimination against blacks or other minority voters.

Under the compromise proposal, a judge could rule that discrimination occurred if actions by state and local officials had the effect, or "result," of diluting minority voting strength. But the measure specifically provides that the law could not be interpreted to require proportional representation.

The results test is considerably easier to prove that the standard in effect since 1980 when the Supreme Court ruled that the law is violated only when state or local officials consciously intended to discriminate.

Until the compromise was agreed to, the administration had pushed for the "intent" standard and argued that a "results" test would lead to proportional representation by race in municipalities all over the country.

President Reagan said Monday that he believed the compromise contained language to prevent that problem.

But Hatch, one of the leading opponents of the compromise, charged yesterday that the agreement is "little more than cosmetics" and will lead to proportional representation. He warned that Congress is about to give "legal and constitutional sanction to a restoration of separate but equal."

East offered unsuccessful amendments to weaken the measure and indicated he will try again when the bill reaches the Senate floor, probably later this month.

He failed to amend the part of the act requiring jurisdictions with a history of discriminatory practices, most of them in the South, to clear beforehand any election law changes with the Justice Department. East had wanted a simplified "bailout" to make it easier for those jurisdictions to be exempted from the law after a period of good behavior.

The compromise would extend the preclearance provision for 25 years, with an interim congressional review after 15 years, and would allow a covered jurisdiction to bail itself out by meeting strict standards of compliance with the act.

Thurmond called the compromise "a step in the right direction," but said he is still worried about the threat of proportional representation and the bailout provisions in the compromise.

The committee voted, 17 to 1, to send the compromise to the full Senate. The lone dissenter was East.

The House voted, 389 to 24, last October to approve a similar bill and is expected easily to approve the Dole-Kennedy-Mathias compromise.