IRVINE, Calif. » Michael Phelps’ run-up to his last Olympics begins with this week’s U.S. national championships. He’s facing his biggest month of the year in the pool, but the challenge is more mental than physical.

The 14-time Olympic gold medalist has competed sparingly so far this season, and hardly gotten the results he’s used to. A month ago in Paris, he struggled in his freestyle events and appeared off form.

"Not being as satisfied as I want to be leaving here I think is more than likely going to happen," he said yesterday. "It’s going to be a meet that is more mental than physical."

There’s a lot at stake when the five-day nationals begin today. The top two finishers in each event qualify for the Pan Pacific championships later this month in Irvine, and from that group, the U.S. team for next year’s world championships will be chosen.

Failing to qualify for those teams means American swimmers won’t be competing at a major international meet until the 2012 London Olympics.

Phelps is scheduled to swim five events in Irvine: the 200-meter freestyle, 100 butterfly, 200 fly, 200 individual medley and 200 backstroke.

His busiest day will be his first, when he competes in two events tomorrow.

"I’m more motivated now than I have been all year," he said. "Not being where you want to be is frustrating. You know what you need to do to get back and you know what you need to change."

Phelps is still perfecting his new freestyle stroke, which was flawed in Paris, where his timing and stroke were off.

"It is a lot better than it was a couple weeks ago," he said. "I feel like I can actually swim freestyle again. That’s always a good feeling coming into a nationals meet."

Many of Phelps’ Beijing Olympic teammates are here looking to solidify their schedules for the next two years.

Ryan Lochte injured his left groin last week, which has curtailed his breaststroke practice. He planned to test the stroke before deciding whether to swim the individual medleys, where he would compete against Phelps in the 200 IM.