In politely worded advertisements, the new ownership of Hialeah Park had notified its customers that jackets are to be worn in the clubhouse. This was one more try at recapturing the essence of Hialeah, and perhaps some of the track's snob appeal before gentile poverty set in further.

It was useless. Within five days, the restrictions were out, and the peopls wer invited to come to any part of the track in any attire that wasn't X-rated. Hialeah's owners are now more sensitive to the number of customers than to their mode of dress. It is a race-track fighting for survival. Its crowds and betting handles have been scarely better than Bowie's.

They still call it. "The World Most E Beautigul Race Track," which it used to be and probably still is. But it has suffered misfortune. The world's most socially spiffy track has wound up as a track on the wrong side of the tracks. The population shift, including the flight of important money far to the north of Miami, has left Hialeah in a bit of a ghetto, distant from the social centers and the great cash flow taht makes a racetrack tick.

Gulfstream, the upstart track up the road in Hallandale, just north of Hollywood, next door to Lauderdale, close to Pompano Beach, Boca Raton, and not that far from Palm Beach is now the favorite Florida track.

The story of FLorida racing in recent years has been the rise of Gulfstream and the fall of Hialeah. "The only salvation for Hialeah," one man has said, "is to put the track on the wheels and move it 30 miles north up the coast."

Hialeah is now virtually a ward of the township of Hialeah. Town officials came to its rescue a few months ago just before the track threatened to vanish. They funded $9 million of a mortagage that enables JohN. J. Brunetti to buy the track from John Gal-breath and his partners for $12.3 million. After only four years, the Gal-breath group gave up on the track for which they paid $21 million, reaping only the joy of telling their tax accountants of their writeoffs.

For his $12.3 million, the 45-year-old Brunetti, a Philadelphian whose family has a racing background bought that stretches for 200 acres just north of the city of Miami. It is an Audubon Wildife Sancturay for migrated birds. It is an aquarium that is a year-round tourist attraction. And it is a magnificent clubhouse-grandstand complex that has won awards for its French Mediterranean architecture.

And it is all in trouble, because the people aren't coming to Hialeah to bet the horses as much as they used to and because the horsemen aren't bringing all their good horses here as they did in the years when New York didn't have winter racing, and when Hialeah was the only operation in the East.

Those were the great days of Hialeah. Its very portals bespoke money. The tall and tufted royal palms that line the quarter-mile driveway to the clubhouse, the manicured boxwood and the splashes of bouganvillea and hibiscus that framed the walkways.

"The special train back to Palm Beach will leave after the seventh race," track announcer Freddy Caposella used to intone every racing day. That special train from Palm Beach was discontinued many years ago when the Palm Beach set seemed to lose interest in Hialech and went off to their yachts and their golf and their tennis, instead.

Earlier this month, after Gulfstream closed, Brunett's attempt to revive Hialech as a track that could show enough betting revenue for the state to regain the valuable midseason dates from Gulfstream did not get off to a very salubrious start.

The new operation did a smart thing by bringing in Steve Cauthen, the young riding sensation from New York, to perk up opening-day interest. It is said, and believed by many, that the track gave Cauthen a $5,000 payoff for his trouble. It proved to be a not bad arrangement. A crowd of more than 22,000 came to the races.

But otherwise, most of the day bordered on chaos. The new management didn't provide programs on time - trouble with the printer - and when the programs did show up the crowd was made more mutinous when it noted the price had been rised to 40 cents. The tracks decided to give the programs away in self-defense, after the first two races were delayed a half-hour each.

The next day, Tommy Roberts, the track's new general manger, whose racing background is mostly in television, came up with a bright idea. He would send for customers if they weren't all that self-motivated to come to Hialeah. He arranged for buses to transport them to the track and back free, from four stragegic locations. They never got started to the track, because the regular bus lines entered a foul claim and Roberts' bright plan collapsed.

The crowds and the betting have fallen off steeply since opening day, perhaps too much to insure Hialeah's survival. The average has been 11,000 and the betting near $1,100,000, which is these days of dollar inflation is not a good number. When Hialeah had the prized January-March middle dates, in 1973, attendance for the 40 days of racing was down more than 225,000 from 20 years before. And betting was $13 million less than in 1969, ominous trends for the once-great track.

There is also is a bit of seediness, now in the appointments of Hialeah. Unparalelled showpieces are the flora and the funa and the infield lakes. But there are some holes in the parking lots that wuld have left track founder Joseph E. Widener in a swoon, and on the rainly day last year some clubhouse patrons had to move from their seats beneath a leaky roof.

They're lucky to have Seattle Slew on the grounds, running in the famed Flamingo, a Kentucky Derby stepping stone. He will draw some extra people on Saturday and help the betting, even if the fans weren't responsive when that unbeaten colt made his 1977 debute last week in a seven-furlong dash before an average crowd of 11,000.