;Senate Majority Leader Robert C. Byrd (D-W.Va.), hinted strongly yesterday that he is about to come out in favor of the SALT II pact, and said he has been urging other senators not to take firm positions against SALT during the current flap over Soviet combat troops in Cuba.

Byrd's remarks in an interview were one of several apparent attempts by friends of SALT II to counter the anti-SALT mood that has spread through Washington since the Carter administration accused the Soviet Union of stationing combat troops in Cuba.

At the White House, officials continued to search for ways to calm the concerns of senators, who seek firm commitments of higher defense spending in 1981 and 1982, without actually commiting the administration to specific spending levels.

The defense spending issue will come to the Senate floor next week in a debate on the budget resolution, and the White House is trying to prevent that debate from turning into a symbolically damaging show of force by SALT II opponents.

Byrd, in an interview yesterday, said he is "about to reach a decision" on the treaty, which he has been studying rigorously for months. Indicating his likely support, he described the treaty as "winnable," and said he wants "to get these undecided senators to slow down and not get rushed to judgment."

Byrd repeated his earlier observation that the flap over Soviet troops in Cuba "is no reason to get panicky or hysterical," adding, "it's easy to cut off our nose to spite our face." SALT is worth supporting, he said, if "it will have a beneficial effect on the security of the country."

Byrd said the opposition of Sen. Russell B. Long (D-La.) to SALT II, announced this week, "did not surprise me." Sen. Alan Cranston (D-Calif.), the majority whip, went further in a separate interview, saying he always expected Long to vote "no." Cranston is an active SALT supporter.

Byrd said President Carter's political weakness has been a factor in the SALT debate, and hinted that Carter should be spending more time on SALT and other legislative matter, and less on political campaigning. "He has problems that need attention here," Byrd said of the president. "The energy issue, defense spending in the budget, SALT, the Cuban situation."

"I'm not saying he's not giving them attention," Byrd said, but added it would be better "if he could give them more time."

"I have always said that the best campaigning is getting your job done," Byrd observed. "People perceive that if an officeholder does his job well and is on the job, they are reluctant to throw him out of office."

The ranking Republican on the Foreign Relations Committee, Jacob K. Javits (N.Y.), released a speech last night that he will deliver today insisting that the Cuban issue should not affect the final vote on SALT II."I believe this issue will be satisfactorily resolved in the next few weeks," Javits said.

Javits said if the Senate vote were held on SALT II now, "It is highly unlikely that it would command the necessary two-thirds vote. Yet I believe that the chances are better than 50-50 that, when it is finally voted on, it will be ratified."

(Two-thirds of the senators must vote for the treaty to approve it.)

Javits indicated, but did not directly declare, his support for the treaty, saying it "can have no material adverse effect" on American security, and might restrain the Soviet buildup while the pact is in effect.

An uncommitted southern Democrat, Walter (Dee) Huddleston (Ky.), said in a speech yesterday that the issue of Soviet troops in Cuba should not be linked to the SALT debate. The troops' presence in Cuba "is a matter of serious concern," Huddleston said, but their removal "should not be made a condition of treaty approval."

Both the White House and Sen. Sam Nunn (D-Ga.), now a key swing figure in the SALT debate, continued to maintain silence yesterday on the contents of an evening meeting Thursday between Nunn and President Carter, which administration officials said could be crucial to the outcome of the SALT debate.

Knowledgeable sources said Carter had urged Nunn not to commit himself publicly in the near future, and there were indications that the senator would comply.

A hopeful Carter administration official said last night that "the crisis atmosphere (set off by the Cuban flap) has begun to calm down," noting that Long's declaration of opposition to SALT II on Wednesday "did not trigger any other announcements" from other senators.