Sen. John W. Warner (R.-Va.) urged his Senate colleagues yesterday to postpone a decision on SALT II until after next year's presidential election so that ratification of the treay can be a major campaign issue.

While Warner insisted that his call for delay did not mean he has decided to oppose the treaty, Senate Majority Leader Robert C. Byrd (D-W. Va.) told Warner that "delaying action on this treaty kills it."

Warner responded that he would "never be a part of using delaying tactics as a means to defeat the treaty." The debate should not stop, Warner said, but should become "one of the two or three major issues" of next year's campaign.

Warner, the fourth-ranking Republican on the Senate Armed Services Committee, did not say what he would do if the treaty comes to a vote before then. The White House reportedly has hopes that Warner eventually will vote to ratify the second strategic arms limitations treaty.

His Virginia colleague in the Senate, Independent Harry F. Byrd Jr., has announced he will vote against the treaty.

Neither Maryland senator, Republican Charles McC. Mathias, nor Democrat Paul S. Sarbanes, has taken a position on ratification.

During a 45-minute Senate speech and discussion that followed it, Warner said yesterday that "fate of the treaty will determine, in large part, the course of our national defense policy for the next decade. Therefore, every effort should be made to gain widespread public support because . . . a clear perception is emerging that we must strengthen our national defenses across the board. This will require greater public support and funding for defense."

Warner also said public opinion polls "depicting an administration of steadily declining influence" make it questionable whether the Carter administration can either overcome senatorial objections to the treaty or will accept changes necessary to win its approval.

The presence of Soviet combat troops in Cuba has stalled deliberations, Warner said. He noted that there is no fixed date for either the Foreign Relations or Armed Services committees to wind up their consideration of the treaty, or for floor debate to begin.

If action doesn't occur soon, Warner said, the Senate will find itself trying to act on the treaty in a year "dominated by campaigns for the presidency as well as for a third of the Senate."

By delaying a vote until after the election, Carter "will be able to use the campaign as a forum for repairing his damaged credibility," Warner said.

"If he (Carter) wins reelection, he will have regained the strength and leadership he will need to bring about ratification of the SALT II treaty in some form acceptable to the Senate.

"If, on the other hand, some new president is in the White House in 1981, he will have arrived there on the basis of a campaign in which the SALT II treaty and the broader issue of national defense were major factors. He will be dealing from a position of mandated leadership and strength not only with the Senate, but with the Soviets as well," Warner concluded.

Majority Leader Byrd said SALT II "will be a campaign issue" regardless of when the vote on it occurs in the Senate. "Let's dispose of the treaty," Byrd told Warner.Delay, Byrd warned, will only permit Russia to build more weapons that would be banned by the treaty.