BOSTON — He leads the Red Sox in RBI, and thanks to his three-run homer in the second inning of last night’s rout of the Tampa Bay Devil Rays, he leads them in home runs, too.

He’s their best defensive infielder and in a day or so, will probably find out that he will be the American League’s starting third baseman in the All-Star Game on Tuesday.

He could also be a free agent in a just a few months, yet strangely, that’s generated little angst among a fan base that seems genetically predisposed to worry about the future.

What more, exactly, does Mike Lowell have to do?

From the time he became a member of the Red Sox, he was seen as an expensive throw-in, the necessary anchor the Sox had to saddle themselves with if they wanted his teammate, Josh Beckett.

If the Sox wanted Beckett, the prospective ace, they had to take Lowell and his $18 million in remaining salary. With some reluctance, the Sox agreed.

Eighteen months later, the money seems a relative bargain, particularly when matched against the money given to less productive third basemen — think Adrian Beltre ($11.5 million) or Scott Rolen ($12 million).

Per Red Sox policy, there’s been no attempt to negotiate a new deal during the season. Both sides have agreed to wait until the fall to discuss Lowell’s future.

Lowell has made it clear, again and again, how much he enjoys being a member of the Red Sox. He appreciates the franchise’s history and relishes the atmosphere at Fenway — as might be expected from someone who languished in front of miniscule crowds in south Florida for years.

All things being equal, Lowell would like to remain with the Red Sox. He thrives at Fenway, carrying a .357 home batting average even before last night’s career-first five-hit effort. He fits effortlessly into the clubhouse, comfortable with Latin and U.S.-born players alike. Moreover, the team figures to be competitive and the opportunity to win championships — Lowell has one from the 2003 Florida Marlins — is enticing.

But Lowell will likely have to sacrifice money and security to stay put. Anything more than two years wouldn’t interest the Red Sox, who are careful not to lock themselves into long-term deals for players heading into declining years. And if Lowell is looking for a big raise from his current $9-million average annual value, he will probably need to seek it elsewhere.

(Lowell’s history of second-half dropoffs — career numbers before the All-Star break: .281-102-389; career numbers in the second-half: .264-61-269 — also understandably spooks the Sox somewhat).

If , on the other hand, Lowell wants his best chance at a mega-contract, his timing couldn’t be better. This season figures to be his best, offensively, since 2003 — with a big series in Detroit this weekend, he could come close to already matching his RBI total of a season ago — and his defense remains superb.

There’ll be little competition among third basemen: For now, Mike Lamb is the next most attractive prospective free agent.

Thin at most positions in the upper reaches of their farm system, the Red Sox have no obvious replacement for Lowell in the minor leagues. Neither are there many options on the free-agent market, unless one counts Alex Rodriguez, almost certain to opt-out of his deal with the Yankees to seek great fortune on the open market.

The Sox’ lone in-house solution would seem to be moving first baseman Kevin Youkilis across the diamond to his original position at third.

That move would only create another vacancy at first, although, by definition, it’s easier to find serviceable first basemen then third basemen. Sean Casey and Mike Sweeney head the list of a mediocre field at first, but available-by-trade options could include Mark Teixeira, Paul Konerko, Dan Johnson, Richie Sexson, Todd Helton and Chad Tracy.

Of course, the Red Sox don’t know how any of those players will handle playing in Fenway’s hothouse environment, a not insignificant factor in personnel decisions (see: Renteria, E.). There are no such questions surrounding Lowell, a known commodity.

By nature of his quiet, professional approach, Lowell seems unaffected by the uncertainty. He’s not worried about whether he’s returning for 2008.

But maybe the Red Sox should.

smcadam@projo.com