As Sen. Edward Kennedy withdrew from the presidential race and party leaders proclaimed a new "unity," the party was continuing its 12-year-old struggle over national security policy in skirmishes all the way from Madison Square Garden to Kennebunk, Maine.

While trying to ignore the presence of the Russian Bear, the 3,300 delegates in New York were preparing to act as a deliberative body to decide whether the most important new weapons system of President Carter's administration, the MX mobile missle, should be condemned. Meanwhile, two high administration officials were arriving in Maine to soothe Secretary of State Edmund Muskiehs fury, worked up by McGovernites in the State Department, over Carter's nuclear strategy.

The delegates will leave New York with the post-Vietnam split papered over at best, or possibly ruptured further. That split dwarfs the philosophical division on display last month at the Republican convention over equal rights for women. On the transcendent issues of foreign policy, the Republican Party is united behind Ronald Reagan; on those same issues at Madison Square Garden, the Democrats were no less divided than they have been ever since their tormented 1968 convention in Chicago.

Amidst perfunctory assaults on Reagan and pro-ERA demonstrations, an initimation that the United States is in a world struggle with the Soviet Union was delivered to unlistening delegates by Sen. Daniel Patrick Moynihan. He chose an expedient rhetorical device, coined by the late Sen. George Aiken, who said of Vietnam: claim victory and get out. Moynihan's Monday night speech claimed Jimmy Carter has seen the truth of the Soviet threat and is organizing the United States to contain it.

It was not merely that the delegates who struck around after the suspense-ending rules fight Monday night had no interest in Moynihan's warnings about the world struggle. A majority probably did not aprove of Carter's new world posture, as described by Moynihan. The substantial opposition to MX reflects that.

But the dispatch of two aircraft from the Defense and State departments to Muskie's summer home in Maine suggests Moynihan was over-optimistic. With the nuclear-strategy directive signed by the president himself last month, the backfire started at the State Department. Former foreign policy advisers to Sen. McGovern, hired for top ports in Carter's fledgling administration, fueled it. They never have accepted the reality of Moscow's expansionism and have goaded Muskie into outrage over the new policy.

But even Carter's own political advisers are ambivalent about defense and reluctant to accept Moynihan's formulation. Besides seeking to conciliate the Kennedy delegates, they still feel the best way to cut Reagan down to size is to brand him as a warmoner.

The political problem was well put by one of Carter's senior aides here: while a majority of Americans accept the "military superiority" promise of the Republican platform, he believes that that ground can be won in the election by accusing Reagan of resuming an arms race.

All this shows the elements of farce behind the claims of "unity" filling Madison Square Garden. What really exists here is a listlessness, perssimism and lack of passion. "We aren't addressing ourselves to what America is really worried about, a Carter Administration official confided to us on the Garden floor Monday night.

The most important of these worries, whether rank-and-file Democrats fully realize it, is the nation's deteroirating position in the world. It is on this issue that Democrats cannot come to terms.

As compared with this tragic inability of the world's oldest political party to unite on America's place in the world, the withdrawal of Teddy Kennedy was merely a confirmation of Carter's renomination. how to play the Russian threat remains as obscured by the Democrats as it has been since 1968.