Two days after Iowa's Democrats overwhelmingly rejected him, Sen. Edward M. Kennedy met secretly in his Senate office with men whose pleas for a strong national defense he had spurned the past 17 years.

Six prominent defense-oriented Democrats, at Kennedy's request, briefed him on the desperate condition of U.S. defenses contrasted with Soviet might. The senator, carrying an unblemished record of opposition to new weapons systems and military spending increases, listened attentively; he offered no arguments but asked detailed questions.

One day later, Kennedy cancelled a four-day swing into New England and substituted a make-or-break speech at Georgetown University on President Carter's newly hawkish-sounding foreign policy. Unsubstantiated reports spread around Capitol Hill that Kennedy was ready to attack Carter as a warmonger. But that would run counter to his secret defense briefing.

This points up the dilemma of Teddy Kennedy's so far calamitous run for president: he would best fit the national mood by following the advice of his defense briefers; but that conflicts with the views of his closest political advisers, his own record and perhaps his basic inclinations.

The depths of Kennedy's political decline are gauged not by his 2-to-1 loss in Iowa but by deterioration in his New England heartland. Sen. Abraham Ribicoff has been going around Washington saying Kennedy trails Carter badly in Connecticut. That's nothing, Speaker Thomas P. O'Neill told Ribicoff; Teddy is behind even in Massachusetts!

Naturally, then, Kennedy's New Hampshire backers admit he trails in that state's Feb. 26 primary, whose loss would surely end his campaign. Once the dimensions of the Iowa defeat were clear, they told Kennedy headquarters that he must abandon his mushy Iowa rhetoric and tell New Hampshire voters exactly how he differs from Carter.

At this point, on Jan. 23, the six infrequent visitors entered Kennedy's office. Five are Democratic members of the anti-SALT Committee on the Present Danger: ex-Treasury secretary Henry Fowler, ex-deputy defense secretary Paul Nitze, ex-undersecretary of state Eugene Rostow, Harvard professor Richard Pipes and Washington lawyer Max Kampelman.

The sixth man was a senator whose defense record has diametrically opposed Kennedy's: Henry M. Jackson, long belittled as the quintessential Cold Warrior by the smart Washington salons that favor Kennedy. Nevertheless, Jackson prefers Kennedy over Carter and has urged him to go left of the president domestically and right of him on foreign affairs.

Nitze and Rostow spelled out to Kennedy how much it would take to build back U.S. power, particularly in naval forces. No arguments from Kennedy, who asked how much the defense budget should be increased. Jackson contended a national production line will be necessary.

Kennedy asked: how can Soviet power be off-set? The reply from the assembled experts was that it cannot happen overnight but requires a defense buildup over many years. Nobody was impolite enough to point out the role played by Kennedy's Senate votes in creating the present crisis.

To follow the advice of Scoop Jackson and friends, Kennedy would have to jettison his facile formulation given on the Iowa campaign trail when asked to comment on more defense spending: "More is not better. Less is not better. Better is better." Word for word, that follows advice privately given by arms-control ideologue Adam Yarmolinsky when asked how Kennedy could handle defense spending questions.

The acrobatics of bounding from Yarmolinsky to Jackson seem all the more difficult considering the feeling in Kennedy's inner circle that Carter has been recklessly provocative toward Moscow. But Jackson also worries about the president's saber-rattling, considering the lack of a real saber in the U.S. scabbard. The same point was made by another defense-oriented Democrat, Sen. David Patrick Moynihan, in a Jan. 10 speech to the Senate.

Moynihan warned about wielding "a fantasized power" that today does not exist, pointing up that "the counsel of restraint in foreign affairs must come from those who have been depicted in the recent past as the most bellicose." Yesterday Moynihan, writing in The New York Times Magazine, attacked Carter from the left domestically (specifically, on aid to New York City).

Thus, Moynihan has provided Kennedy both with a rationale for a harder line that would solve his defense dilemma and a more radical domestic stance that would quiet his liberal backers -- a formula that might well prove his only hope.