The Cosmos may, at present, be a unique phenomenon in United States soccer, but a phenomenon they are. As an occasion, their double victory Sunday night in Giants Stadium was extraordinary.

More than 76,000 people thronged that spendid arena, admirable in every way except that bane of soccer players, AstroTurf. The gold-clad cheerleaders seemed feeble and peripheral; the huge crowd created its own vivid atmosphere, its own vibrant response to the event.

An event; yet not an event. True, the Cosmos, thanks to a couple of shocking defensive errors and a small field, had gone down to defeat in Tulsa. If the Cosmos win, it is expected of them; should they lose, they are execrated. Thus, a little team from out of town, like Tulsa, finds itself rather in the position of Christians in the Colosseum.

And, now, once again, the Cosmos find themselves facing elimination from the playoffs after losing the first game of their playoff series to Vancouver, 2-0, Wednesday night. They meet the Whitecaps today at 2 p.m. (WJLA-TV-7) at Giants Stadium and must win the regulation and so-called "minigame" to advance to the finals. A sellout crowd is anticipated today.

How remote seemed the days of 1967 when the two rival pro soccer leagues uneasily started. Yankee Stadium was distinguished by its infinite empty seats, and the voice of John Pinto, the New York General president, boomed alone through the awful silence.

The Cosmos have not built a great team, merely an amalgam of great players. Let this not be despised. Against Tulsa, there were things that happened on the AstroTurf -- yes, even on the AstroTurf -- that were breathtakingly fine. Franz Beckenbauer, once captain of West Germany, may stroll about now, but to see his beautiful, effortless, curving passes, hit with the outside of the right foot, skim uneringly across the field is exhiliarating. Exhiliarating, too, was the way he once casually juggled with the ball, before putting it perfectly to a colleague.

The sharp, neat turn with which Giorgio Chinaglia left David Nish of Tulsa -- and once England -- for dead to score one of his goals was excellent, too, as were the ebullient runs (however self-indulgent) and the beautifully headed goal by Brazil's Francisco Marinho.

Yet it was an American, little Rick Davis, who impressed me as much as anybody. He is the first native-born American soccer player I have seen with the skill, imagination and intelligence to prosper at the highest level. On this largely senatorial team -- Johan Neeskens is always ready to run, others much less so -- Davis is a vital ingredient. He is quite tireless, generous with his stamina, and above all, enormously intelligent in movement.

There are things I dislike about the NASL: its ludicrous 35-yard offside rule, for a start, allegedly designed to mitigate the effects of narrow fields. There are few of these now, and all the rule does is to distort the game, and condemn NASL players to operate under different rules from the rest of the world, imposing painful, if occasional, adjustments.

That a league should terminate in a playoff, after a season of competition, seems a silly contradiction to me. But if we must have playoffs, they could surely be more rational. A smiling Phil Woosnam, commission of the NASL, crowed in the Cosmos dressing-room afterwards that the game and the subsequent "minigame," had proved the validity of the practice.

I disagree. It was all very well when a team which lost, 3-0, as Cosmos had earlier in the week, leveled their goal aggregate in the return game against Tulsa, but what of last year when the Cosmos lost, 9-2, in Minnesota yet still got through to the Soccer Bowl final by winning the return and the minigame? By rights, they should have been eliminated on goal aggregate.

Woosnam's answer to that was that had it not been for the NASL system, the Cosmos would not have surrendered so easily in Minnesota. My own feeling is that their victory last year was tarnished.