Senate Majority Leader Robert C. Byrd (D.W.Va.) said yesterday that the Strategic Arms Limitation Treaty "is very much alive and kicking" and will come up for a vote in the Senate "early next year," despite speculation that the pact has lost momentum.

The majority leader went out of his way to assure reporters that just because he has postponed debate on SALT II until 1980 doesn't mean that the treaty is dead.

Byrd conceded it may be difficult to obtain the two-thirds vote needed for Senate approval and that some senators may not make up their minds until an hour or two before the actual vote.

But he said postponing the debate does not mean he has given up hope or decided to let the treaty stay on the Senate calender indefinitely without a vote.

"The Senate will reach a vote on this treaty early next year, make no doubt about, "Byrd said. "It is my top priority early next year."

Byrd added he is aware there is speculation that the treaty is all but dead, and that many observers believe it is substantially short of a two-thirds vote at present and isn't gaining new support very rapidly.

But he pointed out: "the Panama Canal treaties were pronounced dead. The natural gas bill was pronounced dead. The windfall profits bill was pronounced dead even before it was sent up to the Senate and the house. We've seen these premature, illconcieved prognostications before."

Byrd said, "I have no reluctance to bring this up just because the outcome is uncertain. The outcome has been uncertain and will be uncertain until the final vote. It is through the debate itself that the votes are decided."

On another matter, Byrd said he is growing impatient with delays in Seante passage of the windfall profits bill, and especially with the plans of some seantors to re-offer amendents that already have been defeated.

Byrd said he may offer a debate-limiting cloture motion early next week, insisting, it's time to fish or cut bait."

He attacked some tax-cut amendments being offered by senators, such as one propose by William V. Roth (R-Del.) that was defeated by a vote of 49 to 44 last week, as "budget bustrs" loaded with "demagogurey," and politically irresponsible."

He warned that if the windfall tax and Chrysler aid bills do not clear the Senate by the planned Dec. 21 adjournment date, he will cancel the proposed long year-end vacation and bring the Senate back the week after Christmas, and again "right after New Years's day" to finish.

Byrd again warned that unless the oil companies support a windfall profits tax that the public perceives as "fair and equitable," they may find price controls reimposed on oil. President Carter now is phasing out such controls.

Byrd said he favors "slapping controls back on" unless a good windfall tax bill is passed, and said, "I hope the president will . . . leave no doubt he'll slap controls back on."

Byrd stressed that while he has always opposed moves to break up the big oil companies, as a result of the industry's opposition to windfall taxes "I'm not sure I'm not changing my attitude on horizontal and vertical diverstiture."

Byrd sidestepped an invitation by reporters to criticize Sen. Edward M. Kennedy (D-Mass.) directly for criticizing the shah.

Byrd said, "The issue is this: 50 American hostages in Iran. The issus is not the shah (or) the crimes of the Ayatollah Khomeini -- let's keep our eye on that ball. I support the president 100 percent."

Byrd in recent weeks has said repeatedly that action on SALT II has been delayed by the need to finish the energy and windfall tax bills first and the fact that the Iran crisis has diverted senator's attention from the treaty.

When Byrd announced last week that he was postponing debate on SALT II until next year, informed Senate observers said the reason was that the treaty only has about 53 to 55 backers now, with little prospect of getting the required 67 votes in the foreseeable future.

These sources feel that Carter's prestige will have to rise dramatically, either through a successful outcome of the Iranian crisis or some sharp boost in his general popularity, before the administration can win Senate approval of the treaty.

At his press conference yesterday, Byrd did not discuss a precise vote count, but maintained that there are enough undecided votes to put the treaty across. The seantor sought to dispel any notion that he has given up hope on SALT II or is indefinitely postponing debate on it.

"It's tough," he said, "it will be tough sledding, I've said that from the beginning (but) there's no mountain to which there's not a top."