SEATTLE — It’s official: Ken Griffey Jr. is coming back to the Seattle Mariners in 2010. The outfielder, who will be 40 on Nov. 21, has reached a one-year agreement to play his 22nd year in the major leagues.

The Mariners made the announcement Wednesday morning.

The contract figures are expected to be similar to last year, when Griffey earned $3.15 million in a contract that included incentives for attendance and playing time. His base salary in 2009 was $2 million, but it’s possible the base might be slightly higher this year.

“I’d like to thank the Mariners organization for inviting me back to play in 2010,” Griffey said in a news release. “While 2009 was an awesome experience for me, my ultimate goal is for the Mariners to get to and win the World Series. To that end, I look forward to contributing in any role that (manager) Don (Wakamatsu) sees fit on the field, and any manner I possibly can off the field.”

When 2009 ended for the Mariners, Griffey’s future was one of their big questions, but it has now been answered.

Griffey is the fifth-leading home run hitter in major-league history with 630. He’s 30 behind the next man on the list, Hall of Famer Willie Mays, whose guidance a year ago helped steer Griffey back to Seattle when he was also seriously considering the Atlanta Braves.

This time, however, the decision apparently came down to his family being OK with Griffey playing one more year, and the Mariners being comfortable with his role. Griffey is likely to have a reduced role after serving last year primarily as the team’s left-handed designated hitter in a platoon with Mike Sweeney. Griffey’s agent, Brian Goldberg, has said that neither money nor playing time would be an issue for his client.

“We believe that Ken’s presence with the Seattle Mariners organization was such a positive asset last season with his leadership on and off the field,” said Mariners GM Jack Zduriencik in the release. “His passion for baseball, life and the Seattle Mariners goes unsaid. We are happy to have Ken back for the 2010 season.”

Griffey was still a teenager when he broke into the majors with the Mariners in 1989, the son of former Cincinnati Reds “Big Red Machine” outfielder Ken Griffey Sr. and the No. 1 pick in the 1987 draft.

During his initial stint with the Mariners, he became one of MLB’s iconic players, a featured star in Nike’s ad campaigns and perennial All-Star, winning the American League’s Most Valuable Player Award in 1997. He hit .304 that year with 56 homers and 147 RBI — one of five seasons in which he hit 45 or more home runs. He also participated in the signature moment in franchise history, scoring the winning run from first base on Edgar Martinez’s double in the clinching game of the 1995 Division Series against the Yankees at the Kingdome.

However, after the 1999 season, Griffey requested a trade to be closer to his family, and was eventually dealt to the Reds in a deal that brought Mike Cameron, Brett Tomko, Antonio Perez and Jake Meyer to the Mariners.

Griffey’s second stint with the Mariners may have been set in motion in June 2007, when he received a hero’s welcome during a three-game interleague series between Seattle and Cincinnati at Safeco Field.

Last year, Griffey’s fate remained undecided until after spring training opened, but on Feb. 21, he chose the Mariners over the Braves. Griffey was given considerable credit for improving a clubhouse that had been riddled with dissension the previous year.