Lou Boudreau, the Hall of Fame shortstop who both managed the 1948 Cleveland Indians and played inspired shortstop to lead them to their first American League pennant in 28 years and the World Series championship, died yesterday at a hospital in Olympia Fields, Ill. He was 84.

He was taken to St. James Hospital and Health Centers yesterday in cardiac arrest and was pronounced dead, said Julie Miller, a hospital spokeswoman. He was hospitalized last month for circulatory problems, forcing him to miss the Indians' 100th anniversary celebration honoring their top 100 players.

Boudreau was once known as the Boy Wonder because, at age 24 in 1941, he became the youngest manager in major league history. He had been the Indians' regular shortstop for two seasons when, in November 1941, the team fired its manager, Roger Peckinpaugh.

Boudreau applied for the job. ''I was only 24 years old at the time, with just four seasons of professional ball behind me,'' he later recalled. ''I figured I had nothing to lose because I didn't tell anybody about it -- not even my wife.''

He wrote a letter to Alva Bradley, the Indians' owner. ''I told him I was qualified to handle the job,'' Boudreau said. ''I thought he might ignore it. Instead, he called me into a meeting of club directors.'' It was determined that the Indians needed young blood, and Boudreau got the job, shocking the baseball world.

For his first few years, the best that Boudreau the manager could do was help make Boudreau the player better. In 1944 he led the American League in hitting with a .327 average. He also led the league's shortstops in fielding percentage, assists, putouts and double plays. In his first six years as manager, however, his team never finished higher than third and finished in the second division three times.

Bill Veeck took over as owner of the sixth-place Indians in 1946. ''My first problem,'' Veeck wrote in his book ''Veeck as in Wreck,'' ''was that the best shortstop in baseball was, in my opinion, not the best manager.'' He added, ''I particularly wanted to get Louie out of the manager's office'' -- and retain him as the shortstop -- ''because I had Casey Stengel waiting in the wings, ready to sign.''

But the reaction to removing Boudreau was so strong -- newspaper columnists condemned the change, and more than 16,000 letters of protest from fans inundated Veeck's office -- that Veeck backed off. ''Louie held all the cards, and he knew it,'' Veeck said.

Boudreau remained manager. It was among the best decisions Veeck ever made. In 1948, the Indians contended for their first pennant since 1920 with an assortment of outstanding players: outfielder Larry Doby, the first black player in the American League; Bob Feller and Bob Lemon, the ace starting pitchers; everyday stars like second baseman Joe Gordon, third baseman Ken Keltner and catcher Jim Hegan; and the legendary Negro league pitcher Satchel Paige, who was added in midseason.

''It was quite a year,'' Boudreau recalled. ''The pressure kept building and building, until I thought we'd all burst.''

Bill McKechnie, who had managed three different teams to pennants, had been hired as a Cleveland coach at Veeck's suggestion, and, Boudreau said, ''was a big, big help to me.''

''I have never known another year like the one we had in Cleveland in '48,'' McKechnie said. ''Every day was like a final game of the World Series. And that year, Lou Boudreau was the greatest shortstop and leader I have ever seen.''

Boudreau batted .355, second best in the league, and he drove in 106 runs, hit a career-high 18 home runs, struck out just 9 times in 560 at-bats, led A.L. shortstops in fielding and was named the league's most valuable player. And he called the shots from the bench and from the field.

After the last game of the regular season, the Indians and the Boston Red Sox were tied for first, setting up a one-game playoff on a chilly afternoon at Boston's Fenway Park.

Boudreau made the unexpected move of skipping Feller and Lemon and starting the 28-year-old rookie left-hander Gene Bearden, with only one day's rest, against a lineup stocked with left-handed power. ''Bearden was one of the finest competitors I had ever known,'' Boudreau said.

Bearden pitched a five-hitter and Cleveland won, 8-3. Boudreau went 4 for 4: he homered over the left-field wall in the first inning, singled in the fourth to begin a four-run rally, homered again in the fifth and later singled again.

The Indians went on to beat the Boston Braves in the World Series, four games to two, with Boudreau batting .273.

His greatest thrill as a player beyond the playoff game, he said, was helping to end Joe DiMaggio's 56-game hitting streak in 1941. DiMaggio hit two smashes down the third-base line, which Keltner stopped, throwing him out. On DiMaggio's last chance to keep the streak alive in the eighth inning, he grounded a ball up the middle and it took a bad hop. ''But I was able to get it and threw him out,'' Boudreau said.

After the 1950 season, with his skills diminishing and with the Indians having finished fourth, Boudreau was traded to the Red Sox, ending a nine-year managerial reign. He played in 82 games for Boston in 1951 and was named the manager the following year, his last as a player. He managed the Red Sox through the 1954 season and managed the Kansas City Athletics from 1955 to 1957. He then became a WGN radio and television broadcaster for Chicago Cubs games, and in an unprecedented move changed places with Charlie Grimm, the Cubs' field manager, on May 4, 1960.

Boudreau returned to the broadcasting booth after that season.

None of the teams he managed after 1948 finished higher than fourth.

Boudreau became known for a 1946 managerial move called the Williams shift, used against Ted Williams, who was a left-handed pull hitter. Boudreau, seeking to throw him off balance, put all four infielders between second base and first and moved the center fielder into right field -- only the left fielder remained on the left side of the field -- daring Williams to hit to the opposite field. Williams would not concede and wreaked considerably less havoc on the Indians than in previous years.

''There is no doubt,'' Williams said, ''that the shift hurt me.''

Louis Boudreau was born in Harvey, Ill., on July 17, 1917. He first made his athletic reputation as a basketball player, leading Thornton High School to the Illinois state championship in 1935, then becoming the captain and star guard at the University of Illinois before leaving to sign with the Indians.

Boudreau, at 5 feet 11 inches and 185 pounds, had average size, an average arm, less-than-average speed and small hands. But he had deceptive talent, competitive zeal and a good mind. His lifetime batting average was .295, and his wide-ranging skills led him to be inducted into the Baseball Hall of Fame in 1970.

At the induction ceremony were his wife, Della, and their four children, the youngest of whom was Sharyn McLain, wife of Denny McLain, a longtime major league pitcher.

Boudreau retired as a sportscaster in 1988, after 30 years. In the mid-1990's, he moved to Frankfort, Ill., about 35 miles west of Chicago.

His baseball legacy remains with a plaque in Cooperstown. ''It's something you dream of and think about,'' Boudreau said when elected to the Hall of Fame. ''This is what we all strive for -- to reach the top.''