It used to be that when a great fight was about to happen, an appropriately anticipatory crowd would assemble. Authors, entertainers and knowledgeable fight fans of every description used to flock regularly to Madison Square Garden and its earlier incarnation on New York's Eighth Avenue. As long ago and far away as that was, the influx of the fight crowd and an electric pre-fight atmosphere that was part of those times is being repeated here on the eve of Saturday night's title unification battle between two brilliant 26-year-old welterweights with perfect records, Oscar De La Hoya and Felix Trinidad.

Las Vegas thrives on replicating places and eras. One can imagine arriving in Tuscany or Monte Carlo or ancient Egypt by walking into one of the massive hotels on The Strip, as long as the illusion isn't spoiled by such discrepancies as the "Eiffel Tower" standing next to Ballys. Fight promoters, like other entrepreneurs, have thrived here -- built boxing's mecca in the desert -- by selling hard and even bending the truth in the name of fun and profit. But the De La Hoya-Trinidad fight has needed no creativity. It is that Las Vegas rarity, the genuine thing.

It harkens to the decade-ago battles among Sugar Ray Leonard, Marvelous Marvin Hagler, Thomas Hearns and Roberto Duran, and before that to Sugar Ray Robinson and his array of classic foes, Carmen Basilio and Jake LaMotta among them -- when the action was not confined to the heavyweights. To equal some of those historic nights, De La Hoya-Trinidad would have to be a war. But that is what this fight promises to be. Both are heavy hitters who tend to get hit. Both have been knocked down -- Trinidad six times, De La Hoya four -- but they have never failed to gather themselves quickly and return more fire than they took.

The betting is even at Mandalay Bay, the fight site, where both weighed in this evening at precisely the limit, 147 pounds. De La Hoya is a slight favorite at most other sports books. This fight is a bettor's nightmare, a fan's delight and a cauldron of nationalistic fervor. Trinidad, nicknamed "Tito," bleeds for Puerto Rico. De La Hoya was quick out of the Los Angeles barrio after he struck gold at the Barcelona Olympics, but he has since retraced some of his steps and won over fellow Mexican Americans dismayed by his Hollywood glitz and Mexicans slow to embrace him because he twice smashed their fistic idol, Julio Cesar Chavez.

Trinidad, 35-0, isn't as well known in the United States as Chavez because he speaks little English and spends most of his time at home with his family, while De La Hoya has been marketed expertly by promoter Bob Arum. But Trinidad boasts a potential advantage in this fight: He is virtually a middleweight lurking as a welterweight, and he hits like a middleweight. Having defended his International Boxing Federation title 14 times over six years, he has been ready for some time to move up from the 147-pound weight class. In contrast, De La Hoya, 31-0, has been World Boxing Council 147-pound champion only 2 1/2 years. De La Hoya also is about to move up in weight, but at 5 feet 11 Trinidad is bursting with size and straight-ahead power from a strong right hand.

De La Hoya can offset Trinidad's strengths with the experience of more marquee matchups, ring cunning and knockout power in his left hand. He is fast and slick. A left-hander as a small boy, De La Hoya was quickly turned around in his neighborhood gym by a man named Joe Minjarez. Minjarez also began to develop De La Hoya's right, also forceful. But as he grew up, De La Hoya maintained a skillful jab and a Hall of Fame hook that often travels mere inches. A shade shorter than Trinidad, he likes to crouch and move. He can double up on his hooks, to the head or body. He can dance, saying he will step right to avoid Trinidad's straight right. And seizing every opportunity as Leonard did at his best, De La Hoya will go for an opening in a flash or for a wound without mercy.

In choosing opponents, Arum has brought De La Hoya along carefully to a peak in 1999. Until he won a split decision over Ike Quartey in February, De La Hoya usually took on an opponent who had to come up in weight to get the fight or was on the downside of his career. Guaranteed $21 million Saturday night to $8.5 million for Trinidad, De La Hoya will surpass $100 million in career earnings. His wealth banked, De La Hoya this week espoused his one remaining major goal. "I want to make history," he said.

Trinidad and his father-trainer, Felix Sr., are reminiscent of Hagler and his people before the 1987 fight with Leonard. The Trinidads appear so confident it's as if they have never considered losing. Overconfident beyond reason, the Hagler crowd gave Leonard no chance and lost. But Felix Sr. knows what great opponents can do; a boxer himself, he was knocked out in 1979 by talented featherweight Salvador Sanchez.

Don King hovers as Trinidad's promoter but is secondary to Arum in this venture. Amid his own wild laughter, King told Arum the other day: "When Tito wins this fight, we'll be happy to draw up the exact same contract -- except that we'll put Trinidad's name where De La Hoya's name is now and my name where your name is."

De La Hoya vs. Trinidad

What: Oscar De La Hoya vs. Felix Trinidad in a 12-round

welterweight unification title bout.

When: Tonight (undercard begins at 7:15 EDT). Main event expected to begin between 11:30 p.m. and midnight.

Where: Las Vegas.

TV: Pay-per-view (coverage begins at 9 p.m.).

Records: De La Hoya 31-0, 25 knockouts; Trinidad 35-0,

30 knockouts.

Ages: Both are 26.

Purse: De La Hoya, $21 million; Trinidad, $8.5 million.