Senate Majority Leader Robert C. Byrd, normally an accurate weathervane of congressional sentiment, yesterday predicted the Senate will approve the Panama Canal treaties next year.

Byrd, making his most optimistic assessment to date, said he personally remains uncommitted on the treaties but "barring some unforeseen development, I think they'll be ratified."

The West Virginia Democrat, who recently led a Senate delegation to Panama, conceded that "if the vote were taken right now" the treaties would be defeated. But he quickly added that "in due time" the American public and the Senate will come around to supporting the pacts.

Byrd told his weekly news conference on Capitol Hill that Panama leader Omar Torrijos warned senators who visited him last month that he would have "difficulty controlling the situation if the treaties weren't ratified within four or five months.

The matter came up, Byrd said, when he'd asked what would happen if a vote on the treaties were put off until 1979, as some senators had suggested.

"His reaction was one of great concern," Byrd said. "The country needs badly, in his view, to have the treaties ratified."

Torrijos, he said, warned that "social problems" and economic difficulties would arise if the treaties were delayed.

Torrijos told the seven-member Senate delegation that uncertainty over the treaties had already slowed economic growth in the Central American nation "to about zero" and caused unemployment and retarded business investment.

Declaring "it would have been foolhardy" to have brought the treaties up for a vote this fall, Byrd said he expects the treaties to come before the full Senate in late January or early February. He foresess a month of debate on the issue, during which he expects a "statement of understanding" to be attached to the treaties.

In early October, Byrd worked behind the scenes to persuade President Carter to seek a similar statement of understanding from Torrijos which reaffirmed U.S. rights to defend the Panama Canal. He later said the agreement saved the treaties from Byrd's assessment differed markedly from one offered by Sen. Barry Goldwater (R-Ariz.) in an Atlanta speech Friday. Goldwater said he sees little chance of Senate approval, and no chance if the U.S. Supreme Court rules that the House of Representatives also must consent.

In the same speech, however, Goldwater took the unusual step of sharply attacking fellow conservative Republican Ronald Reagan for criticizing the treaties during his presidential campaign last year.

"In my opinion, he was getting very close to the position of a presidential cadidate declaring war," Goldwater said. "I don't think any man elected to the office of President should go in with the idea that he is committed to war."