Willie Hernandez, the star left-handed relief pitcher for the world champion Detroit Tigers, was named the American League's most valuable player today. Kent Hrbek of the Minnesota Twins was a surprising second in the voting.

A 28-year-old native of Aguada, Puerto Rico, Hernandez is the fourth American Leaguer and the seventh pitcher overall to win his league's MVP Award and Cy Young Award in the same season.

Hernandez, who received 16 first-place votes and was named on 27 of the 28 ballots, won the award with 306 points. Hrbek had 247 and relief pitcher Dan Quisenberry of the Kansas City Royals got 235.

"After last week, winning the Cy Young Award, a lot of the people were telling me I was the one who was supposed to win this," said Hernandez, who was reached at his grandfather's home in San Juan. "But it's unbelievable, winning these two awards in the same year for a relief pitcher . . . It was like I have another win, like winning the World Series again.

"I feel very proud of myself. I know the people in Puerto Rico feel very proud. Puerto Rico deserves it. We have a small island, but a lot of people play baseball in Puerto Rico. It's going to give them more respect.

"We have had Orlando Cepeda, Roberto Clemente, people like that. But I don't know how many pitchers we have had to win awards like that. I don't think any."

Hrbek was the only player named on all 28 ballots, one voter passing over both Hernandez and Quisenberry because of his belief that an everyday player, rather than a pitcher, should receive the MVP Award given annually by the Baseball Writers Association of America.

Following the top three were the Baltimore Orioles' Eddie Murray with 197 points, the New York Yankees' Don Mattingly with 113 and the Tigers' Kirk Gibson with 96.

Hernandez, who began the season with a 34-32 record in the majors, was 9-3 this year, with a 1.92 earned-run average and 32 saves in 33 times in which a save was possible.

He got the final outs in the Tigers' division-clinching victory, the last game of the AL playoffs against Kansas City and the final game of the World Series against San Diego.

He was acquired by the Tigers from the Phillies March 24 along with first baseman Dave Bergman for catcher John Wockenfuss and outfielder Glenn Wilson and played a major role in the Tigers' 35-5 start that left their AL East rivals behind only six weeks into the season.

In his entire previous career, beginning in 1977, Hernandez had acquired only 27 saves, and his best previous season was 9-4 with a 3.28 ERA with the Chicago Cubs and Phillies in 1983. He had eight saves with those teams in 1983.

Previous pitchers to win the AL's Cy Young and MVP honors in the same season were Denny McLain of the Detroit Tigers in 1968, Vida Blue of the Oakland A's in 1971 and reliever Rollie Fingers of the Milwaukee Brewers in 1981.

National Leaguers who have won both in the same season were the Brooklyn Dodgers' Don Newcombe in 1956, the Los Angeles Dodgers' Sandy Koufax in 1963 and the St. Louis Cardinals' Bob Gibson in 1968.

Fingers is the only other relief pitcher to win an MVP Award in either league.

Rounding out the top 10 were Tony Armas of the Boston Red Sox, Winfield, Alan Trammell of the Tigers and Willie Wilson of the Royals.

Twenty-eight players were named on at least one ballot.

Baltimore's Cal Ripken Jr., last year's AL MVP with 322 points, received just one 10th-place vote, and one point, this year.