The new magic word at the White House is "bipartisanship," a concept and a slogan that President Reagan's advisers view as a way of linking national security and political strategies in advance of the 1984 campaign.

Their long-term goal is to recreate a semblance of a foreign policy that "stops at the water's edge," to use a phrase familiar to the president since his days as an internationally minded liberal Democrat.

In the short run, this bipartisanship promises a payoff that includes deployment of the MX missile, passage of the Caribbean Basin Initiative and continuation of a significant measure of military aid to El Salvador. Less likely, though possible, is passage of a defense budget that would give the president at least 60 percent of the increases he is seeking.

In the customarily optimistic Reagan scenario, the Soviets will be persuaded by congressional support of the MX to bargain seriously on strategic nuclear weapons and subsequently will be persuaded by deployment of Pershing II and cruise missiles in Europe, beginning in December, to negotiate an agreement limiting these intermediate-range nuclear weapons.

Reagan would then be able to campaign in 1984 as an Eisenhower-style "peace candidate" after co-opting the Democrats on the very issue where he has been most vulnerable. The idea commends itself to the rival power centers in the Reagan White House, including the national security apparatus headed by William P. Clark and the politically minded White House staff led by James A. Baker III.

"This is a political plus for the president in the campaign," White House communications director David R. Gergen said. "The country by and large is far more interested in hearing that Washington is working together than in partisan contentions. It would also mean a better chance to pick up the support of blue-collar workers, who are supportive of many of these foreign policy goals."

The political value of this approach has not been lost on the president. Reagan may ramble or display an embarrassing lack of detailed knowledge about his programs when he meets with senators or is pressed by reporters in an extended interview, but his sense of political timing remains keen. Last week, for instance, he was quick to make a personal thank-you call to AFL-CIO President Lane Kirkland for supporting the MX.

"Bipartisanship," as a political strategy, has expedient utility for the administration. It also has the potential to divide the Democrats, already in disagreement among themselves on Central America and the MX. Even more, however, it can be used to portray Reagan as a would-be peacemaker trying his best to strike a deal with the Soviets, notwithstanding his massive defense buildup and U.S.-backed covert activities in Central America.

Presidents have reaped dividends from the peacemaker approach since Woodrow Wilson was reelected in 1916 on the slogan "He Kept Us Out of War." In Richard Nixon's case the equivalent, while a war raged in Vietnam, was opening U.S. relations with the People's Republic of China.

Reagan's advisers believe that the same goal may be accomplished if he is seen as seriously seeking an arms control agreement with the Soviets.

A byproduct of the new bipartisanship has been a temporary rekindling of "happiness" talk among the feuding factions in the White House. One senior aide calls it "a de facto burying of the hatchet." Though some in the White House still think that "burying the hatchet" means an act of aggression against a rival, the political imperatives have combined with Reagan's unwillingness to make staff changes and molded an official, if uneasy, truce.

A principal architect of the truce and the bipartisan approach to Congress has been deputy national security adviser Robert C. (Bud) McFarlane, a former Marine and House staff aide who has spent much of the last two weeks listening to members of Congress and trying to persuade them that Reagan's commitment to arms control is more than a fig leaf for the MX.

McFarlane says that he was "shaken out of my executive upbringing" by the prospect of obtaining a bipartisan agreement on MX. In fact, he is the son of a New Deal Democratic congressman from Texas. What McFarlane means by that statement, however, is genuine for he has lately come to understand that Congress needs to be listened to, consulted and reassured if it is expected to go along with the president in his foreign-policy adventures.

Not even the staunchest admirers of Clark and Baker depict either as an arms-control specialist, so the role of explaining policy has fallen to McFarlane. It is a role unlikely to end with the now-expected congressional approval of the MX.

"If we're to establish a new consensus, there must be an act of faith on both sides," McFarlane said in an interview last week. "Congress must put aside partisan attacks on national security. On our side, we've got to follow up, and we've got to listen. There must be on our part credible evidence of serious interest in arms control." Reaganism of the Week: (At the signing ceremony for "Baseball Month" on the south grounds of the White House Wednesday): "Well, this is more fun than being president. I really do love baseball, and I wish we could do this out on the lawn every day."