New York's Flushing Meadow Park was once the Valley of Ashes, its ugliness memorialized by F. Scott Fitzgerald in ''The Great Gatsby.'' Though the ashes are gone, what remains is a flat tract surrounded by freeways that is only lightly used. The inferior soil is subject to flooding. Two world's fairs have left temporary buildings behind. Once-pleasant walkways have sunk into the ground. The lake's rowboat concession is inactive.

This is not, in short, a very grand park, and thus it is not scandalous for promoters to propose using it for three days each year for Formula One Grand Prix auto races. Such races might create a certain excitement and stimulate a certain amount of economic activity.

Nevertheless, just because the races would not desecrate shabby Flushing Meadow is no reason to approve them. The city's possible gains from converting the park do not offset the risks, costs, noise, traffic jams and public inconvenience involved. The Mayor's concessions review committee would be wise to reject it.

The most likely effect of turning the park into a race course would be to clutter the Parks Department's agenda and distract its staff. Particularly at professional levels, they are already spread too thin. Triumphs like the reconstruction of Central Park's Belvedere emphasize the department's unmet challenges: the unfinished rebuilding of the Wollman Skating Rink, the graffiti-covered buildings that still disgrace Brooklyn's Prospect Park, the neglect of Forest Park in Queens. The list could go on and on.