By Steve Keating

OMAHA, Nebraska (Reuters) - Michael Phelps, one of the world's most recognizable athletes, will lead a crop of new faces to Rio as a week of ruthless competition at the U.S. Olympic trials ended on Sunday and shifted the focus to the Summer Games pool.

Phelps and old foe Ryan Lochte, the 31-year-old pillars of U.S. swimming who between them have amassed 33 Olympic medals, will again provide the foundation for a 45-member squad that will be a mix of experience and youth.

At one end of the spectrum are Phelps, who will compete in his fifth Games and Lochte his fourth. At the other extreme are 30 Olympic newcomers.

Out, are Olympic champions, Tyler Clary, Matt Grevers, Cullen Jones and Natalie Coughlin.

In, are a wave of first time Olympians, including Maya DiRado who qualified in three events.

"Going forward we are going to have to step up to a new level and we will see some new faces step up at the top," said Bob Bowman, Phelps' coach who will also be in charge to the U.S. men's team in Rio.

"We have our tried-and-true guys and I think with Michael and Ryan we're going to be able to count on them but it's going to be very exciting to have a new group of guys step up ... and kind of take us into the next era of swimming."

Swimmers arrived in Omaha declaring the pressure of the U.S. trials was far greater than anything they face at an Olympics but monstrous expectations will weigh heavily in Rio where the stage is bigger, the spotlight brighter and the competition tougher.

With thumping rock music, pyrotechnics, flaming geysers and capacity crowds of over 14,000 filling the CenturyLink center for every session the U.S. trials offered up exceptional entertainment but in the end delivered more flash than substance.

The trials failed to produce a single world record while just one American mark fell.

The meet finished with only two American men, Josh Prenot (200 breast) and Ryan Murphy (100 back), at the top of the world rankings, and just two women in Katie Ledecky (200, 400, 800 free) and Lilly King (100 breast) atop the lists.

Many of the winning times were slower than those four years ago at the London trials, a puzzling development that neither Bowman nor women's coach David Marsh could explain.

"One of the things we have always done well, better than anyone else, is improve from the trials to the Games," said Bowman.

"I'm confident we will do that again, we have a great plan in place and quite frankly we are going to have to do that if we are going to have the kind of Olympics we expect to have and want to have."

That warning hit home loud and clear on Saturday when Australia’s Cate Campbell powered to a world record in the 100 meters freestyle at the Brisbane Grand Prix.

Even Phelps, heading for his fifth Olympics, acknowledged times will have to improve dramatically between now and the opening of the Rio Games on Aug. 5 if he is to add to his haul of 18 gold medals.

"I think it's going to take a lot faster times," said Phelps after winning the 200 medley. "There are always fast times that are swam throughout the world.

"I do understand that I have to swim faster to have a chance to win the gold medal; I do know that."

Having qualified in the 100 and 200 fly and 200 medley and a candidate for the relays, Phelps, already the most decorated Olympian of all-time, will expect to add to his staggering medal haul.

For the last three Summer Games, Phelps has shouldered plenty of the load but now 31 and having dramatically scaled back his agenda, the U.S. will have to count on big contributions from others if the Americans are to confirm their status as swimming's super power.

The best American shots at gold in the pool will come from the team's youngest member 19-year-old distance queen Ledecky.

Ledecky could leave Brazil as one of the breakout Olympic stars as she tries to complete a rare gold medal hat-trick in the 200, 400 and 800 freestyle.

"Hopefully I think they're going to be scared! I mean, it's no secret that we're going to be there towards the end," warned a defiant Lochte.

"I think the Japanese, everyone, Brazil, Hungary, we've all been racing against each other so many times that we know it's going to be a dog fight till the end.

"The U.S. is not easy to beat, and we're going to definitely prove that in Rio."

(Editing by Andrew Both)