Senate Majority Leader Robert C. Byrd said yesterday he will try to define for the Soviet leadership the role of the U.S. Senate in the SALT II treaty ratification process when he meets with Soviet President Leonid L. Brezhnev in Moscow later this week.

Byrd also promised to let the Soviets know that the Senate "is not going to vote for the treaty out of fear" and that Brezhnev's appeals against Senate changes are not "helpful" in winning support for the strategic arms pact.

"I don't think its helpful for the Soviets to be issuing statements about dire action that might follow in the wake of senate decisions," Byrd said. "I hope to make this clear to the Soviets when I'm there."

Byrd was referring to Brezhenev's warning in Vienna that any attempts to change or alter the SALT II treaty would have "grave and even dangerous consequences." Carter administration officials have all but conceded that Senate passage of SALT II is unlikely without at least some modest alterations.

Byrd said when he goes to Moscow on Thursday, via Italy, he will explain to the Soviets the differences between passage with reservations, "sense of the Senate" resolutions, and outright amendments to the treaty. "I want them to have a better understanding of the Senate's role," he said.

Speaking to about a dozen reporters amid the high-ceilinged splendor of the majority leader's Capitol office, Byrd still withheld his own judgment on the SALT II pact. But the West Virginia democrat, who will have a pivotal role in the ratification debate, had some strong words, for his colleagues who have spoken out for amending the treaty.

"The air is so filled with talk of modifications already. One might get the impression that there really is no reason to have any debate, that we shouldn't hold any hearings - just take the vote next week," he said."It's entirely too early to discuss amendments to the treaty.... The Senate ought not to be intimidated by slogans or catchy rhetoric."

Byrd said, "Any senator who talks about amendments ought to be asked what amendments he has in mind." He said the treaty is so complex that it requires "more than one reading," and he displayed for reporters his own copy of the text, complete with his own underlining in red, notes in the margins, and question marks by unclear passages.

"As of this point, this senator is not going to talk about any amendments," Byrd said.

Yesterday was the majority leader's weekly meeting with journalists, that gives the West Virginia country lawyer his traditional Saturday morning forum to espouse on the issues of the day like an elder statesman. While most of yesterday's session was devoted to SALT, the senator did manage to deliver comments on energy, aid to Turkey, and the Senate's record going into mid-year.

The senator characterized the first half of this year's Senate session by the slow, measured pace with which some "landmark legislation" has been debated and passed. Byrd said he believes this Congress, and particularly this Senate, has mirrored the electorate's mandate of last November for fiscal restraint.

Specifically, Byrd said that by reducing the federal budget deficit by $21 billion "Congress has been reflecting that mood of budgetary restraint."

Byrd said that the amendments to Senate rules at the beginning of this session has limited filibusters and delays and helped keep the Senate on the schedule that he himself set. "I think the thrust has been right, the emphasis has been right," he said.

According to his schedule, Byrd said the Senate should be able to vote this summer on energy legislation that Sen. Henry M. Jackson (D-Wash.) is promoting, as well as moving on hospital cost containment legislation, "some kind of national health insurance, be it catastrophic or other," and a trade bill.

By that schedule, Byrd said, the Senate should "then be ready to begin on the SALT treaty, which is just the most far-reaching legislation of all, by Oct. 1." The Senate Foreign Relations Committee will begin 20 days of hearings on SALT on July 9, and the Armed Services Committee will begin separate hearings July 23. Final committee reports will be due Sept. 25. CAPTION: Picture, SEN. ROBERT C. BYRD...will go to Moscow this week