WASHINGTON — Manny Acta was hired by the Washington Nationals yesterday, making him the youngest manager in the major leagues.

The 37-year-old Acta, a coach with the Mets the past two years, replaces 71-year-old Frank Robinson, who was told during the final week of the season that he wouldn’t be back.

The Nationals went 71–91 in 2006,finishing in last place in the NL East for the third consecutive season. New ownership, led by team president Stan Kasten, is overseeing an overhaul of the team in hopes of being competitive when Washington’s new stadium opens in 2008.

“We have a very good plan in place here. We’re going to do it the right way,” Acta said. “We’re going to be patient, and we’re going to bring a winner here, sooner (rather) than later.”

Acta will lead what could be an inexperienced roster next season, although he does know some Nationals veterans: He worked as Robinson’s third-base coach with the Montreal Expos from 2002–04, before the franchise moved to Washington.

“Everyone who’s been with him has raved about him,” Kasten said. “He came in here probably more prepared than any candidate we had, knowing our roster, knowing the holes in our roster.”

Acta agreed to a two-year contract with two one-year club options.

While Robinson was a Hall of Fame player who hit 586 homers, then managed in the majors for 16 seasons, Acta’s playing days ended in the minors and this is his first job as a big league manager.

“Frank was more of an old-school guy. We’re going to have to wait and see how it’s going to be with Manny,” said Nationals catcher Brian Schneider, a member of the Expos during Acta’s tenure. “He’s young. He’s motivated. He’s waited to do this for a long time. He knows the game of baseball.”

Said third baseman Ryan Zimmerman: “You go from a guy who has 50-something years in the game to a guy who’s just started. It’s going to be quite a different feel, but I think Manny will do just fine.”

Acta has managed in the minors and in the Dominican Winter League, and he led the Dominican Republic to the semifinals at the World Baseball Classic this year.

During that tournament, Acta benched a struggling Alfonso Soriano — the All-Star who hit 46 homers and stole 41 bases for the Nationals in 2006 and has filed for free agency. Acta said Soriano was the first player who called to congratulate him on being hired by the Nationals — although the new manager indicated he figures the size of a contract offer will have more to do with where Soriano winds up.

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The Mets have so much confidence in 41-year-old Orlando Hernandez, they’re ready to keep him for two more seasons.

Hernandez and the Mets agreed yesterday to a $12 million, two-year contract, filling a spot in an aging New York rotation that was ravaged by injuries during the team’s playoff run last season.

El Duque, acquired from Arizona in May, went 9-7 with a 4.09 ERA in 20 starts for the Mets. He was in line to start the team’s playoff opener against the Los Angeles Dodgers before injuring his calf while jogging in the outfield.

Hernandez, who turned 41 last month, gets a $1 million signing bonus, $4.5 million next year and $6.5 million in 2008.

“There’s a lot of guys out there right now close to his age that are pitching well,” general manager Omar Minaya said at the GM meetings in Naples, Fla. “The way the marketplace is, I didn’t think it would be realistic to sign Orlando Hernandez for one year. He stays in shape. He’s a hard worker. If you wanted to get him, you were going to give him two years.”