WASHINGTON - While the Phillies plot their offseason strategy, one question will be how far into the future Chase Utley can be counted on to be a valuable contributor.

It's a difficult question to answer, made more complicated by Utley's surprising durability this season at the age of 35.

He's already a franchise icon, one of the most respected athletes to ever play in Philadelphia.

While his knee problems have been well documented, Utley made one trip to the disabled list last year, and that was for an oblique injury.

And for all he has accomplished this year, including becoming an all-star for the first time since 2010, what has been truly impressive is that Utley has stayed away from the disabled list.

His contract for next season would increase $5 million, to $15 million, with 15 days or fewer on the disabled list this year because of knee injuries.

Utley hasn't been on the DL at all.

"He has been very durable, and that is something a lot of people didn't think would happen," bench coach Larry Bowa said. "He's got a routine he goes through and is very regimented and dedicated to what he does."

In addition to next year's contract, there are vesting options from 2016 to 2018.

So it's possible Utley could be 39 and still in the Phillies' plans.

But will he be able to continue to withstand the grind?

This year Utley batted .355 with a .978 OPS in March and April. He hit .291 with an .830 OPS in May. It went to .240 and .616 in June; .268 and .735 in July; and .243 and .691 in August.

"The baseball season is a grind," manager Ryne Sandberg said when asked about Utley's possibly wearing down. "He is still getting quality at-bats and quality games."

Then Sandberg pointed out a simple fact about competing in the homestretch of baseball's regular season.

"Players are often tired in the sixth month of a baseball season, but in his case I will monitor that and probably make some adjustment," Sandberg said.

Both Sandberg and Bowa pointed out how taxing on the body it is to play a middle-infield position.

"Guys are constantly trying to knock you out on double plays, you are covering bunts, going out for cutoffs, relays, covering the bag on steals, and it is a stop-and-go position," Bowa said. "It is not easy on your legs, and he has been very dedicated in the commitment he has made to play the position."

There also has been speculation about eventually moving Utley to first base. He has made 22 career starts at first, but hasn't started there since 2008, when he did so twice.

"If anybody could do it, he could, but it is not something you just throw him or anybody over there," Bowa said. "That position takes skill."

Bowa acknowledges that playing first doesn't take as much toll on a player's body.

"I don't want to say it is an easier position, but it is easier physically," Bowa said.

Added Sandberg: "I am real pleased with the way Chase is moving around the field and putting in the number of games."

Saturday marked Utley's 130th start, and he has appeared in 134 of the first 141 games. That exceeds last year, when he started 124 games. In 2011 and 2012, he averaged just 90.5 starts per season.

Heading into Saturday, Utley was batting .277 with 30 doubles, five triples, 11 home runs, 72 RBIs, and a .764 OPS.

Those are strong numbers for a second baseman. One person they don't measure up against is Utley in his prime.

What's easy to forget is what an extraordinary four years Utley had from 2006 to 2009, when he hit .303 with a .924 OPS. He averaged 29.5 home runs, 39.5 doubles, 115 runs, 100.5 RBIs, and 152 games.

Utley isn't likely to return to those levels, but he can still be a major player if this season is an indication.

The key for the Philies is projecting how long this stellar play can last and whether it will be at second base.

mnarducci@phillynews.com

@sjnard