Timely Writer, one of the nation's outstanding 3-year-olds, was destroyed after breaking his left foreleg and causing a four-horse spill in the $563,000 Jockey Club Gold Cup today. The race was won by Lemhi Gold, who is now all but assured of winning horse of the year honors.

In addition to Timely Writer, the 2-to-1 favorite in today's race, 50-to-1 shot Johnny Dance also was destroyed.

The mishap occurred at about the 1 1/8-mile mark. Island Whirl, who broke from the 11 position to lead up to that point, was being chased by Lemhi Gold and Timely Writer. Timely Writer's left foreleg suddenly snapped, throwing jockey Jeff Fell. Timely Writer was hurdled by Sing Sing, who threw his jockey, Miguel Rivera. The two trailing horses, Khatango and Johnny Dance, both slammed into Sing Sing and also fell.

"My horse broke his leg and I heard it, so I knew right away," said Fell, who was unhurt. The only jockey injury was a cut chin suffered by Ruben Hernandez, on Khatango.

Dr. William Reed, who this spring paid $3 million for half interest in Timely Writer for stud purposes, said, "I felt that Timely Writer was a cinch today. He was perfectly sound, in my estimation. I'm speaking as a vet as well as part owner."

Timely Writer, who had been favored to win the Kentucky Derby before he was sidelined by abdominal surgery, was to have been retired to stud after the Gold Cup. Dr. James Beldon, a physician for the New York Racing Association, will perform an autopsy and postmortem of both horses Sunday.

Timely Writer's death ended a melodramatic racing career. He was a virtually unknown colt who sold for $13,500. His sire, Staff Writer, ended his days on an Idaho cattle farm. Timely Writer won last year's Champagne Cup to cast him into racing's forefront. He fell just short in balloting for 2-year-old horse of the year.

He returned as a 3-year-old to win the Flamingo and Florida Derby before encountering stomach ailments which required surgery.

He was sidelined four months, but returned Aug. 14 to win Suffolk Downs' Yankee Handicap and followed with a $32,000 allowance victory at Saratoga. A 2-to-1 favorite in the Marlboro Cup three weeks ago, Timely Writer started slowly and finished 25 lengths behind winner Lemhi Gold.

Today's mishap obscured a solid, if unspectacular performance by Lemhi Gold, who won New York's richest racing event by 4 1/2 lengths in 2:31 1/5, the slowest winning time since the race was shortened to 1 1/2 miles in 1975.

Lemhi Gold ran the race that trainer Laz Barrera and jockey Chris McCarron wanted. He waited patiently behind the quick pace set by Island Whirl, who ran the first half-mile in 47 3/5 seconds. Lemhi Gold passed Island Whirl with three-eighths of a mile to go and never was threatened.

By winning the $339,000 first prize, Lemhi Gold joins Budweiser Million winner Perrault as the only $1 million winners this year. He returned $7.20, $4.20 and $2.60. Silver Supreme, ridden by Angel Cordero Jr., made up five lengths in the stretch and finished second, paying $4.80 and $3.00; Christmas Past, the field's lone filly, ridden by Jacinto Vasquez, paid $3.60 for third.

Island Whirl was unable to keep pace, and finished fourth, 23 lengths behind. Runaway Groom, owned by Albert Coppola of McLean, Va., was fifth.

"The race went just the way we planned," Barrera said. "We wanted him to go out and lay second. It's a long race, a mile and a half; you can make a mistake if you make a horse go too early.

"There is no doubt in my mind that this horse is horse of the year," Barrera said. "He has proven he could win on grass or dirt."

In the $240,000 Champagne Stakes, which immediately preceded the Gold Cup, Fred W. Cooper's Copelan removed any doubt that he is the nation's finest 2-year-old with an easy 6 1/2-length victory.

The 4-to-5 favorite saved ground behind Total Departure and What's Dat, caught them just past a half mile and went past on the outside under the mild urging of jockey J.D. Bailey. He was never challenged, finishing a mile in 1:37 4/5.