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NEW YORK (Reuters) - Trevor Hoffman, the most prolific closer in Major League Baseball, has decided to retire after an 18-year career.

The 43-year-old relief pitcher, whose 601 regular season saves remains an MLB record, told the sport's official website (www.mlb.com) Tuesday that he was calling it quits to take up an administrative role with the San Diego Padres.

"It's time to retire. It's time to move on," Hoffman said.

"This is more of a self-evaluation. I expect to pitch at a certain level and I had to be honest with myself that I wasn't certain I could maintain that anymore."

A formal announcement from the Padres about his new job was expected Wednesday.

The right-handed Hoffman, a master of change of pace, spent most his career with the Padres, recording 552 of his saves between 1993 and 2008, but left as a free agent after the club decided not to renew an option to re-sign him.

"I understand that some of it is about baseball being a business, but I don't really want to rehash all that," Hoffman said. "There's been a turnover of people there who wanted to reconcile and I've been cool with it. A couple of years definitely makes a big difference."

Hoffman spent his last two seasons with the Milwaukee Brewers and had a 2-7 record in 2010 with 10 saves and a 5.89 earned run average, well above his career ERA of 2.87.

Hoffman surpassed Lee Smith's MLB record of 478 saves in 2006 and became the first pitcher to reach the 500 and 600 barriers. His career total could be tested by the New York Yankees' Mariano Rivera, who has 559.

"Some guys leave the game and they really don't know. But for me, having a commitment from the organization I made my name with is pretty big," Hoffman said.

(Reporting by Larry Fine; Editing by Frank Pingue)