Senate Majority Lesder Robert C. Byrd (D.W.Va) took the occasion of his weekly meeting with reporters yesterday to aim a stern lecture at the Japanese government for maintaining "most unfair" trade barriers that limit U.S. exports to Japan.

Criticizing the Japanese cabinet's announcement last week that there will be no further concessions to U.S. trade negotiators, Byrd warned that "if the Japanese hang tough... this country can hand tough, too.

The majority leader also said he would not go along with some White House political advisers who had hoped that the Senate debate on the strategic arms limitation treaty (SALT) could be delayed until the primary election season next year.

On the trade question, Byrd noted that "trade is two-way street, but... Japan isn't making it a two-way street." If the Japanese remain firm, Byrd observed, "We don't have to buy Japanese automobiles. We don't have to buy their radio sets and television sets, their motorcycles and their tape recorders."

Byrd meets with reporters over coffee in his ornate Capitol office almost every Caturday to discuss pending Senate business. Yesterday he had prepared to talk extensively about SALT, but when he notice a Japanese reporter among his questioners, he devoted about a third of the hourlong sessing to criticism of the Japanese trade stance.

Accordingly, Byrd urged administration officials not to give in on any trade matters when the Japanese prime minister, Masayoshl Ohira, comes to Washington this week to meet with President Carter.

U.S. and Japanese officials have been negotiating for months on steps to reduce Janpan's large trade surplus with this country. Last week, after negotiations aimed at increasing Japanese government purchases of U.S. goods broke down Ohira was quoted by Japanese reporters as saying that Tokyo would make no further compromises.

Byrd said his concern stemed in part from the decline in Japanese purchases of American coal. Coal is an important product of Byrd's home state.

On SALT, Byrd made it clear that he wanted the press to carry a message from him to the White House: He will not cooperate with administration hopes to make the Senate debate a "showplece" of Catter's reelection campaign.

"I've noticed with considerable interest," Byrd said, "that some political pundits and strategists are saying... this debate might be some sort of political showcase next year. But the strategists... don't set the Senate schedule."

Byrd, who is largely responsible for scheduling Senate business, said the debate "should not be designed to help any presidential candidate," because "this should be the least partisan of all issues."

Byrd said he expected Carter to sign SALT with the Soviets within a few weeks, although he did not think it would be done before the end of May.

He said he expects the Senate, which must approve the treaty before it becomes effective, to complete work on it by the end of this year. The only situation in which that would be unlikely, he said would be if U.S. and Soviet negotiators take until October or later to reach agreement.

Byrd, who has been a loyal supporter of Carter on most issues, said he has not yet decided whether to support SALT. He said he will review the pact, when it is completed, in light of one central question: "Are we better off with this agreement than with no agreement at all?"

The senator took issue yeaterday with a Washington Post editorial Friday that rapped him for criticizing airlines that have cut service to West Virginia.

He said the editorial was inaccurate in suggesting that his complaint stemmed from his personal inconvenience. "I can get to West Virginia, and I can get back." Byrd said.

The editiorial missed the "overall point," he said -- "that airlines should not act unfairly or irresponsibly under deregulation.. If they act responsibly. we'll take our lumps from them like anvone else."