By Steve Keating

OMAHA, Nebraska (Reuters) - Katie Ledecky sent expectations soaring with her first swim of the U.S. Olympic Trials on Monday while Michael Phelps, the meet's other star attraction, was a no-show in the 200 metre freestyle.

Ledecky, who has an ambitious bid to qualify for the 200, 400 and 800 metre freestyles and chase a rare triple gold sweep at the Rio Olympics, cruised into the 400m final with a leading time of four minutes, 2.62 seconds.

The relaxed effort heightened the prospect that she will attack her own world mark of 3:58.37 in the final later on Monday to clinch an Olympic berth in spectacular style.

"Just trying to get those first-race jitters out of the way but hopefully tonight I will use the excitement, have fun and the important thing is getting my hand on the wall first, that's what the goal is," said Ledecky.

Ledecky, 19, has clocked eight of the top 10 swims all-time in the event and also owns the top times in the world this year in the 200 and 800 free.

If another sellout crowd at CenturyLink Arena came expecting to see Phelps they left disappointed after the 18-times Olympic gold medalist scratched from the 200m free.

Instead Phelps, who turns 31 on Thursday, will be left with four opportunities to secure a spot on his fifth Olympic team beginning on Tuesday with the 200m butterfly. He is also entered in the 100m fly, the 100m free and 200m individual medley.

Phelps's great rival Ryan Lochte, however, was back in the pool for the 200 free just 12 hours after the disappointment of a third place finish in the 400m individual medley.

Lochte, who pulled his groin in the 400 IM heats, said he continues to swim in pain but still managed the fifth best effort in the 200m heats clocking 1:47.47.

Conor Dwyer, second in the men's 400m free on Sunday, registered the top time of 1:46.66.

"The turns doing the butterfly kick off each wall I could definitely feel it but I can't dwell on it," said Lochte, an 11-times Olympic medalist. "I feel it right now. I'm in pain but pain is temporary -- I guess."

Backstroke medal contenders Missy Franklin and Natalie Coughlin eased through their 100m preliminaries and smoothly through into the semi-finals.

Olivia Smoliga posted the top time of 59.65 seconds while Franklin, the reigning Olympic champion in both the 100m and 200m backstroke, won her heat clocking the fifth fastest effort of 1:00.09.

Coughlin, bidding to become the single most decorated U.S. female Olympian of all-time, was seventh best with 1:00.75.

"It would be great, that's what my goal is this week (to qualify for Rio). And if I don't, I don't, it's not the end of the world," said the 33-year-old Coughlin, who is tied with Jenny Thompson and Dara Torres as the top U.S. Olympic medal winners among women with 12.

"So I'm enjoying my time racing and we'll see what happens."

(Editing by xxxxxxxxxxxxxxxxxxxx)