The Democratic Platform Committee's journey into fantasy land neared ludicrous heights when committee member Mary Ann Neville of Delaware argued emotionally against draft registration on grounds that "the armed forces are now at 98.5 percent of their authorized strength."

Not one of the committee's 176 other members rose to instruct Neville that the Senate Armed Services Committee 10 days earlier voted to reduce the Army's authorized strength by 25,000 because of too few recruits to fill the ranks. Neville's assault on draft registration, which she claimed would "alienate our youth from the political system," did not pass. But her effort displayed the make-believe mood of party activists who drafted the platform.

That mood fostered much of President Carter's failed foreign and defense policy, but it is now on the verge of popular rejection. However, popular sentiment could not control the platform committee's deliberations at Washington's Mayflower Hotel. Thanks to the rigorous reforms of the past decade, vital organs of the party are insulated from the public will.

"Reality is not this committee's strongest point," a senior White House aide told us. Top Carter aide Stuart Eizenstat and Zbigniew Brzezinski's National Security Council staff worked manfully to stem the lunacy. But with even Carter-pledged delegates addicted to make-believe, it was often a case of "left" v. "lefter." Hence, the Monday night session, which lasted until almost 4 a.m., approved the first homosexual rights plank ever wedged into a major party platform.

The lack of reality showed most not on the social issues that debilitated the party in its reform splurge of the 1970s. This time, left-wing platform architects concentrated on President Carter's current foreign crisis, partly made by the left's own anti-defense dogma.

Outside the platform committee, that dogma is crumbling under the hammer blows of political facts. Sen. George McGovern, one of the Senate's foremost defense-cutters, suddenly favors a new strategic bomber. The ambitious Sen. Joseph Biden told a closed-door meeting of arms control experts on June 18: "I'm damned if I'm going to ride the wrong horse [the new SALT treaty] into the swamp again and sink with it." National strength, Biden said, must come first.

But a careful reading of the party's new platform reveals no such acceptance of reality. The preamble blithely takes credit for a nation "at peace" today. That is a shaky political foundation given the Soviet invasion of Afghanistan, the Marxist advance into the Caribbean and Vietnam's Soviet-backed push into Thailand.

The about-face by McGovern, Biden and other liberal Democrats is dictated by voters back home, who are far ahead of the politicians in judging Carter's foreign and defense policy sins. But on the platform committee, less than a dozen of the 177 members hold elective office and must, therefore, take account of the voters.

The exceptions are Sen. Daniel Patrick Moynihan, Mayor Coleman Young of Detroit (the platform committee chairman), plus scattered mayors, lieutenant governors, aldermen and one county assessor. For the balance, the platform committee reflects not the Democratic Party so much as a few special interests on its fringe who have little interest in a platform made to elect Democrats.

"Where I come from," one of the elective polticians on the committee told us, "the voters know this country is in deep trouble abroad, but this platform contains damn little reassurance of that reality." While Carter tries to cope with the new reality, such defected Carter appointees as former ambassador Dick Clark and former assistant secretary of state Patsy Mink led the attacks on him in the platform committee.

One draft submitted to the committee by platform writers in the Democratic National Committee made this stunning allegation: "The Nixon-Ford administration spent billions of dollars on an imperialist foreign policy which took advantage of the peoples of the Third World." That word "imperialist," parroting one of Soviet propaganda's favored charges against the United States, was too much for the platform committee, which rejected it.

Also rejected (and replaced by an ambiguous compromise) was a total ban on nuclear power plants. On the morning of the platform committee's final work last Tuesday, committee member Elinor Guggenheimer from New York complained that while the Democratic platform committee was condemning dependence on nuclear power, the Democratic president was over in Venice agreeing that "the role of nuclear energy has to be increased."

Were it not for the agitated world situation, such travels in fantasy land by platform writers might pass without notice. Today, however, voters sense the storm rising in the East. They may not that their alarm was ignored by the Democratic platform.