Joe Louis, considered by many to be the greatest heavyweight boxing champion of all time, died yesterday morning in a Las Vegas hospital, the victim of a heart attack.

Mr. Louis, 66, had been in poor health for many years and had been using a pacemaker for five months.

He collapsed at his home at 9:45 a.m. and was pronounced dead of cardiac arrest 20 minutes later at Desert Springs Hospital.

Mr. Louis, who had been confined to a wheelchair since heart surgery in 1977, had attended the World Boxing Council heavyweight championship fight between Larry Holmes and Trevor Berbick Saturday night at Caesars Palace Hotel, where he worked in recent years in public relations for the hotel.

Mr. Louis, known as the "Brown Bomber" for the devastating punches that earned him 54 knockouts in his 71 professional fights, was just 23 when he won the championship by knocking out James J. Braddock in the eighth round in Chicago in 1937.

In 17 years in the ring, Mr. Louis compiled a 68-3 record and earned $4.6 million in the ring. He also successfully defended his title 25 times between 1937 and 1950, including some of the most memorable fights of all time. He held the heavyweight title longer than anyone.

Despite his success, Mr. Louis was plagued by financial problems after his retirement. In 1956, the Internal Revenue Service said Mr. Louis owed the government more than $1 million and he was ordered to pay a flat fee of $20,000 a year until his death.

But nothing could take away from his glory years in the ring. He won his first 28 fights before being knocked out by Max Schmeling of Germany in the 12th round of a nontitle fight in June 19, 1936. After that loss, Mr. Louis said, "I won't be champion until I get that Schmeling."

He did. On June 22, 1938, Louis sent Schmeling to the canvas three times in the first round before referee Arthur Donovan stopped the fight at 2:04.With tension mounting between the U.S. and Nazi Germany, Mr. Louis' victory was immensely popular around the country.

Mr. Louis once said that Billy Conn was the best fighter he ever faced. On June 18, 1941, Mr. Louis knocked Conn out in the 13th round. He knocked him out again, in the eighth round, in a 1946 rematch.

At the age of 34, Mr. Louis announced the first of three retirements. A year later, in 1950, he challenged Ezzard Charles for the title and lost. After a number of exhibitions, he fought Rocky Marciano in 1951 before Marciano became champion. Marciano knocked him out in the eighth round, and Louis quit for good.

"I feel bad about beating Joe," Marciano said then. "Joe was my idol."

Marciano was not alone.