The Bulldog Grand Slam will feature some of the top teams in the country, including Phelps' North Baltimore Aquatic Club and Lochte's SwimMAC Carolina team based in Charlotte.
Phelps, who has captured a record 18 Olympic gold medals in his career, will be competing for the fourth time since coming out of retirement. Lochte is set to return to racing after having complications with his surgically repaired left knee.
The meet, hosted by the Athens Bulldog Swim Club at Gabrielsen Natatorium, was hastily arranged in the past few months to give the top U.S. swimmers a chance to take part in another event this summer before the two more important competitions of the year. The national championships will be held in Irvine, California, from Aug. 6-10, followed two weeks later by the Pan Pacific Championships in Australia.
Those meets will determine the U.S. team for next year's world championships in Russia.
Phelps is scheduled to compete in the 100-meter butterfly Friday, the 100 backstroke Saturday, and the 100 freestyle Sunday. Lochte has entered the same three events, as well as four other races. But it is doubtful the 11-time Olympic medalist will compete in them all coming off knee surgery late last year, especially after his initial comeback was derailed by pain and swelling.
Lochte was injured in November when an exuberant teenage fan ran at him. The swimmer tried to catch her, the two fell over and Lochte hit his left knee on a curb, tearing one ligament and spraining another.
He returned in April for an Arizona meet, but pushed himself a little too hard and had to sit out the final two Grand Prix meets of the season.
The Athens meet will be an important test of how well Lochte's knee holds up, especially if he does the breaststroke. He has entered the 200 individual medley, which includes the breast.
Phelps retired after the 2012 London Olympics, but returned to training last year. He has been steadily building his endurance through competitions and a grueling training session in the Colorado mountains.
Two weeks ago at a Grand Prix meet in Santa Clara, he tied for first in the 100 fly, finished second in the 100 free and 200 free, and settled for third in the 200 IM.
Phelps and Lochte won't be the only big names at the four-day meet in Athens, which begins Thursday. The field also includes Olympic gold medalists Allison Schmitt, Tyler Clary, Cullen Jones, Yannick Agnel of France and Ous Mellouli of Tunisia.
Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.