John McSherry, working the first inning of his 26th season as a major league umpire, collapsed and died in Cincinnati yesterday on the opening day of the baseball season. He was believed to be the first person to be stricken fatally on the field during a major league baseball game since 1920.

McSherry, working behind home plate at Riverfront Stadium, called just seven pitches before walking back toward the stands and collapsing. He never regained consciousness and was pronounced dead at University Hospital in Cincinnati about an hour after the start of the game between the Reds and the Montreal Expos. The hospital said McSherry, 51 years old, suffered sudden cardiac death.

McSherry's death overshadowed the start of what Major League Baseball owners, players and fans hope will be the first full season in three years.

A 234-day players strike curtailed the 1994 season and delayed the start of last season. The first game of this season was played Sunday night in Seattle, but this was to be the first day with multiple games, including the oddity of the Oakland A's opening last night in Las Vegas, Nev., because their stadium is not yet ready.

But bad weather, including snow in Cleveland that put off the Yankees' opener there, abbreviated the schedule. Games were also postponed in Baltimore and Philadelphia, and the game in Cincinnati was called off when players felt they could not continue.

"The team is rattled, very rattled," Ray Knight, the Reds' manager, said at Riverfront. "Nobody wanted to play after seeing something like that happen."

In 1920, Ray Chapman, a shortstop for the Cleveland Indians, died the day after he was struck in the head by a pitch from Carl Mays of the Yankees, but according to the Baseball Hall of Fame in Cooperstown, N.Y., no other deaths on the field or traced to on-field incidents could be recalled in major league baseball.

According to the book "Total Baseball," at least six minor leaguers have died after being hit by pitched balls.

Listed by the National League as weighing 328 pounds, McSherry was the heaviest of the league's 32 umpires. However, the 6-foot-2 1/2-inch McSherry might have weighed even more.

"I think that everybody who saw him in the spring knew how dangerous the situation was getting as far as his weight," Ozzie Smith, the St. Louis Cardinals' shortstop, said after the Mets' opening game at Shea Stadium yesterday. Asked if McSherry looked heavier than he did last season, Smith said: "He was pretty big. He had been fighting that problem for a long time and he succumbed to it."

In Cincinnati, Knight quoted a member of McSherry's umpiring crew as saying McSherry had planned to see someone today about a problem with arrhythmia, an irregular heartbeat.

Knight quoted the umpire Tom Hallion as saying that McSherry was supposed to get treatment earlier but delayed it so he could open the season. "He said, 'I'm going to be here opening day with them and then go get that tomorrow,' " Knight said.

Harry Wendelstedt, the league's senior umpire in his 31st season, said he and his crew working the Mets' game with the Cardinals learned of McSherry's death halfway through the game.

"I think we worked the last half in shock," he said. "It shocks you. I'm trying to bear down worrying about a 3-2 pitch and you find something like this out and it just breaks your heart."

McSherry, a New York native, attended St. John's University and lived in Dobbs Ferry.

Two other umpires died of heart attacks during the season in recent years, but not while working. Lee Weyer, a National League umpire, died in 1988 and Nick Bremigan, an American League umpire, died in 1989.

McSherry had previously suffered a series of medical mishaps during games. Last August he had to leave a game because of heat exhaustion. In 1993, heat again got to him and he had to leave a game. He became dizzy during the seventh game of the National League Championship Series in 1992 and had to leave, and in 1991 he collapsed during a game because of dehydration.

In yesterday's game he watched Pete Schourek, Cincinnati's starting pitcher, retire the Expos' first two batters. After the second pitch to the third batter, Rondell White, McSherry, according to Ed Taubensee, the Reds' catcher, said, "Hold on, time out for a second."

Then he backed away from the plate, waved to Steve Rippley, the second-base umpire, with his right hand, turned away from the field and started toward the gate leading to the umpires' locker room under the stands. Before he reached the gate, he keeled over, falling face down.

The team trainers rushed from the dugouts and doctors rushed from the stands, and they tried to revive him for about 15 minutes as a crowd of 53,000 watched in stunned silence.

He was taken to University Hospital, arriving at 2:40 P.M., and was pronounced dead minutes after 3 P.M.

Katy Feeney, senior vice president of the National League, said the league has no regulations about umpires' weight but said that league officials constantly urge overweight umpires to get their weight down. She said umpires are supposed to have annual physicals, and the league made sure that McSherry had one each year. He had a physical in February, she added.

"They tell us all we're rolling the dice with weight," Wendelstedt said. "It's certainly a thing that hits home, particularly with me, because I carry too much weight around, too."

John Patrick McSherry