Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) asked the Senate yesterday to shut off preliminary debate and get down to business on extending the Voting Rights Act of 1965.

Submitting a bipartisan cloture petition aimed at getting the bill to the Senate floor today after four days of stalled discussion, Baker said he hopes for passage this week.

"The issues that divide the parties on this matter are not great," he said, urging his colleagues to consider carefully the opinions which have been presented. "But there are honest differences of opinion. The amendments are not frivolous ones."

Although the Voting Rights Act extension has 78 cosponsors and several more supporters, a handful of conservative senators led by Jesse Helms (R-N.C.) and Orrin G. Hatch (R-Utah) has sworn to talk "until the cows come home," as Helms put it last week, to get some changes in the measure.

Baker told reporters before the session that he, too, would "prefer to have some slight modifications" but would vote for the bill as it stands. He predicted it would pass "as is or with some minor modifications." Baker had asked the Senate not to try to stop preliminary debate until he returned from a trip to China yesterday and had a chance to meet with all sides.

If cloture is voted today and the procedural "motion to proceed" is passed, the measure is subject to a Helms filibuster that could go into next week.

The Helms group argues that there should be no extension of the part of the 1965 act that is expiring. It is the section that forces nine states and parts of 13 others to obtain approval from the Department of Justice before changing voting laws. Sen. Daniel Patrick Moynihan (D-N.Y.) argued yesterday that such controversy began "a political generation ago" and ought to end now.

"We will pass this bill," Moynihan promised. "There is no way it can be prevented."