The Senate yesterday voted to continue food aid to South Korea in the aftermath of a new agreement allowing congressional investigators to question a key witness in the congressional influence-buying scandal.

In doing so, the Senate rejected an amendment by Sen. Lowell P. Weicker Jr. (D-Conn.) to cut off $56 million earmarked for Food for Peace to Seoul.

Lawmakers heeded an appeal by Sen. Adlai Stevenson (D-Ill.) that the aid was now appropriate because the Koreans finally have agreed to allow questioning of a former ambassador suspected of having made payments to members of Congress.

Last June the House voted to trim the aid allocation from the agricultural appropriation bill because the Seoul government refused to make former ambassador Kim Dong Jo available for questioning. He is suspected of having made or directed illegal cash payment to as many as 10 current House members.

Last week, however, the Koreans agreed to let Kim answer written questions about his dealings with members of Congress.

"Confrontation has produced nothing," Stevenson said. "If his [Kim's] answers the follow up [questioning] that has been promised, then it will be timely to consider reprisals.

House sources agreed yesterday that the Senate vote was appropriate because of the new agreement. They also noted the House might recede in conference committee and allow the $56 million to be restored if Kim's responses are adequate.

The questions might be ready to send to Korea this weekend, one source close to the House investigation said.

The Senate committee also plans to submit questions to Kim, Stevenson said, though - unlike the House - it has no indication he gave money to senators.

Yesterday's Senate vote was marked by a clash between Stevenson and Weicker, who quit the Ethics Committee in a huff earlier this year because the members declined to follow his recommendation to pursue evidence that the Nixon administration covered up the Korean influence-buying campaign.

Weicker accused the Senate Ethics and Intelligence committees of a "resounding cover-up," and said "the American public does not have the whole truth."

Stevenson labeled Weicker's comments as "silly . . . unjustified . . . and perverse." The Senate then voted 71 to 24 to kill the proposed amendment to cut Korean food aid.