The Senate took a slap at Romania for its human rights record yesterday, approving a six-month suspension of trade privileges that allow that communist nation to sell products in the United States at the same low tariffs as noncommunist countries.

The Romanian amendment was added to the massive trade bill on a 57-36 vote on a day when foreign policy issues took precedence over the main objective of the legislation, improving the United States' $170 billion trade deficit.

Senators seemed reluctant to grapple with major trade issues in the bill, and staff aides said most of the more than 100 possible amendments were being held back for next week.

At 7 p.m., Majority Leader Robert C. Byrd (D-W.Va.) stood in the middle of the floor to deliver a tongue-lashing to senators for the lack of action. "What I sense here is a stall," he said. "I'm having great difficulty today and so are the two managers in getting senators to call up their amendments."

He kept the Senate in session late last night and told members to return at 9 o'clock this morning.

While on its foreign policy path, the Senate also voted authority for the president to place limits on trade with Soviet-controlled Afghanistan and three Mideast nations that have been accused of supporting terrorism -- Iran, Libya and Syria.

The measure attacking Romania was opposed by the Reagan administration, which has certified that Romania's human rights record is good enough to qualify it for "most favored nation" (MFN) status.

That status qualifies it for the lowest tariffs the United States offers any of its trading partners, averaging about 5 percent instead of a range between 20 percent and 40 percent for nations not given MFN status. Romania is one of four communist nations qualifying for MFN; the others are China, Hungary and Poland. The measure was pushed by Sens. William L. Armstrong (R-Colo.), Jesse Helms (R-N.C.) and Christopher Dodd (D-Conn.). The opposition was led by Sens. Lloyd Bentsen (D-Tex.), Bob Packwood (R-Ore.) and John C. Danforth (R-Mo.).

Armstrong said the amendment is designed to "make it unmistakably clear to the government of Romania and others . . . that we are dead serious about human rights." He cited a falloff in the number of Romanian Jews who have been allowed to leave that country, and Dodd talked about Bibles that have been made into toilet paper, as examples of Romania's poor record on human rights and religious freedom.

But Bentsen noted that most major Jewish groups oppose the amendment and said, "It will inflict severe pain on families who hope that Romania's MFN status will help them . . . " leave that country.

Bentsen, Democratic floor manager for the major portion of the bill, sponsored the amendment that would deny MFN status to countries that the secretary of State certifies as supporting terrorism. He identified those as Iran, Libya and Syria, and noted that other laws already limit trade with Libya and Iran.

The amendment passed unanimously, and comes as the United States is moving to improve relations with Syria, which is trying to gain the freedom of American journalist Charles Glass, who was kidnaped in Beirut.