Street received 15 of 28 first-place votes in balloting by the Baseball Writers' Association of America and finished with 97 points. New York Yankees second baseman Robinson Cano came in second with 57 points, followed by Tampa Bay designated hitter Jonny Gomes with 39.
Toronto Blue Jays pitcher Gustavo Chacin finished fifth with 14 points, and received two first-place votes.
Street is the second consecutive AL winner from Oakland. A's shortstop Bobby Crosby won the award last season.
Huston Street meets with reporters after winning AL rookie of the year. (AP Photo/Jeff Chiu)
Crosby, Ben Grieve, Walt Weiss, Mark McGwire and Jose Canseco have previously won the award for Oakland. Howard is the fourth Phillies player to win the award, joining Scott Rolen, Dick Allen and Jack Sanford.
The 22-year-old Street became Oakland's main closer after Octavio Dotel went down with an injury. Street finished the season with a 5-1 record, 23 saves and a 1.72 earned-run average.
Street, second in ERA among AL relievers to New York's Mariano Rivera, recorded 72 strikeouts in 78 1/3 innings.
"It's a tremendous honour. Coming into the season my goal was just to stay, one day at a time. Coming out of spring training it didn't even look like I had a chance to make the team," Street said. "Rookie of the year, it's something that's pretty cool; you've got one chance to get it done."
Howard, who led all rookies with 22 home runs, garnered 19 of 32 first-place votes and 109 points. Houston Astros outfielder Willy Taveras finished second with 78 points and Atlanta Braves right-fielder Jeff Francouer was third with 60.
Colorado Rockies pitcher Jeff Francis, a native of North Delta, B.C., was sixth. He received one second-place vote for three points.
Howard really turned it on after replacing injured star Jim Thome by batting .288 with 63 RBIs in 88 games. He had 11 homers and 27 RBIs in the last two months of the season, as Philadelphia came within one game of earning a wild-card berth.
"Things just started falling in," said Howard. "You never want to see anyone hurt or injured, but I just came up and tried to make the most of my opportunity."
with files from Associated Press
