President Carter declared in an interview published yesterday that he will seek Senate approval of the strategic arms limitation treaty (SALT II) "at the earliest possible moment" after the Nov. 4 election even though Soviet troops remain in Afghanistan.

Carter, in the interview with the Associated Press, went further than he has before in separating the fate of the treaty from the issue of the Soviet Union's military presence inside the borders of its neighbor.

Secretary of State Edmund S. Muskie, in a speech last Thursday, separated the future of the treaty from the Soviet invasion more clearly and explicitly than senior administration spokemen had done in the past. At the time he spoke, however, it was unclear whether Carter had agreed to this approach.

Some news accounts noted that the president's public position, as stated in a town meeting in Missouri last month, was that the Senate will be ready to consider the SALT II treaty again "when we see positive movement by the Soviets to withdraw their occupying troops from Afghanistan."

In the AP interview, Carter said he intends to ask the Senate to go ahead with the ratification even if the Soviets remain in Afghanistan. What has changed since last Jan. 3, when he asked the Senate to put the treaty aside, is that "the likelihood or possibility of ratification" has improved, he said.

"When we delayed it before, there was a certainty that had the ratification been brought to a vote it would have been defeated. I think that that certainty of defeat has been removed," Carter said.

The administration drive for ratification of the treaty may have more political than legislative or diplomatic significance at this time. Carter and his aides are trying to draw a clear line between themselves and Republican presidential candidate Ronald Reagan, who opposes ratification on grounds that the treaty fails to limit arms sufficiently and favors the Soviets.

While Carter left open the possibility yesterday that he might ask for ratification by the lame-duck Senate that is to sit for a month following the election, Senate leaders and administration political aides have expressed great doubt that this could be accomplished in such a limited time. It is considered more likely that a new Senate, convening in January, would tackle the issue if Carter is reelected.

Should Reagan be elected, the treaty in its present form will be politically dead.

The GOP candidate has said that he would be willing to undertake new arms negotiations with the Soviets, but at the same time he suggested that a further U.S. arms buildup will be required to improve the U.S. bargaining position.

Administration officials said their efforts to separate the treaty from the Soviet invasion go back to testimony by presidential assistant Zbigniew Brzezinski in August at the Democratic National Convention platform hearings and to the platform subsequently adopted by the Democratic Party. The platform declares that opposition to the Soviet invasion of Afghanistan and passage of SALT II are both in the national interest.

The aides said, however, that new prominence is being given to the issue because of its importance in the presidential campaign. Muskie has been saying publicly for several months that the way to obtain ratification of the treaty early next year is to build a constituency for it in this fall's election debate. Moreover, the high command of the Carter administration is known to believe that the war-and-peace question, especially as it touches the possibility of nuclear war, is Reagan's most important area of political vulnerability.

The effort to bring the strategic arms treaty to the forefront of the campaign, which began with Muskie's speech Thursday to the Women's Democratic Club here may continue in a paid radio address by Carter today, an appearance by Muskie at noon today on "Issues and Answers" (WJLA-TV) and an appearance Monday by Secretary of Defense Harold Brown before Washington diplomatic correspondents.

Also, on Monday, the secretary of state sets out on a two-day round of appearances in Chicago, St. Louis and Milwaukee. While the travel is supposedly "nonpolitical" and thus paid for by the State Department, Muskie is expected to make news in those politically important states with a defense of Carter policies and attacks on positions taken by an unnamed opposition.