By Steve Keating

TORONTO (Reuters) - When Michael Phelps says he sees a bit of his young self in Katie Ledecky, you know you are dealing with a very special swimmer.

Already an Olympic champion, the 19-year-old American distance queen is not exactly an unknown quantity but she could explode into the sporting stratosphere at the Rio Games.

Phelps, competing in his fifth Games and the most decorated Olympian of all time, is the undisputed star heading into South America's first Summer Games.

But when the Olympic flame is extinguished on Aug. 21, it could well be Ledecky left standing in the spotlight, especially if she completes an ambitious program that includes a rare 200, 400 and 800 meters golden hat-trick.

"You can tell she is very goal oriented, and for me it brought me back to kind of what I was like way, way, way back in the day," said Phelps, who will bidding to add to his record Olympic haul of 22 medals, including 18 gold.

"Every time she gets in the water, it's like a world record, so she is improving so much and I think she is just trying to push that barrier.

"I don't see it that much anymore, how hungry she is and every single day she is going in trying to change something and trying to get better.

"It just gives me a lot of good thoughts of what there is to come in the sport of swimming for the younger kids."

The youngest member of the entire U.S. team at the 2012 London Games, 19-year-old Ledecky remains the youngest swimmer in the American squad but returns to the Olympic pool a battle-hardened veteran.

She caught attention of the swimming world in London where at the age of 15 she won the 800 free, now her signature event, and quickly established herself as the new distance queen taking gold in the 400, 800 and 1,500 free at the 2013 Barcelona world championships.

Two-years later at the Kazan worlds she took top spot on the podium in the same three events plus the 200 free.

While she will swim the 200, 400 and 800 free in Rio, the 1500 is not contested by women at the Olympics.

"Every year sort of builds on the next one and you always want to do better the next year than you did the last year," said Ledecky during last month's U.S. Olympic trials.

"I'm always motivated, working toward my goals, and the goals I've had through this year have been the goals that I've been thinking about for the past two, three years, and time to start working and hitting those goals.

"I think four years ago it was all just new and I was doing whatever I was told, and this time I think I feel a little more comfortable."

That is not good news for her rivals.

MATCHING MEYER

This time she is looking to become the first swimmer since Debbie Meyer in the 1968 Mexico Olympics to touch first in the 200, 400 and 800 free. And she could accomplish the rare treble in record smashing style.

There could also be more gold as a member of the U.S. relay teams.

While Ledecky also owns the world records in the 400 and 1,500, in the 800 free she is utterly dominant.

The Olympic and world champion, she has posted the top 10 swims all-time in the event, including the third fastest ever at the U.S. trials.

"Her stroke is something that you don't see too much in women's freestyle," said Phelps. "I think her stroke is phenomenal, how she transitions, and now the walls are great, her kick is great.

"She does the work, and it shows, and I think that is something that is awesome to see and still to see that excitement from the young kids is something that is good for me to see, too."

Ryan Lochte, an 11-time Olympic medalist, told Sports Illustrated that Ledecky "swims like a guy" while Meyer, the first and only woman to win the Olympic 200, 400, 800 free at the same Games, described her to the New York Times as "phenomenal".

Ledecky, though, has made it clear that as far as she is concerned, goals are for her and her alone to decide.

"I'm just going to focus on my racing and what my goals are, and anybody else's expectations don't really mean that much to me."

(Editing by Andrew Both and Nick Mulvenney)