Tapit, the Maryland-based colt many thought to be a threat to Smarty Jones's bid for the Triple Crown, was declared out of the Belmont Stakes yesterday by trainer Michael Dickinson. Trainer Nick Zito also announced The Cliff's Edge will not enter the race.

Three days after Tapit breezed six furlongs on the turf at Dickinson's Tapeta Farm in North East, Md., the trainer posted a message on his Web site saying the horse continues to suffer from the lingering effects of a lung infection discovered in March.

Since being diagnosed with debris in his lungs after finishing sixth in the Florida Derby, Tapit rebounded to win the Wood Memorial in April and finish ninth in the slop in the Kentucky Derby.

"He came out of the work [Wednesday] seemingly okay, but not 100 percent," said David Fiske, racing manager for Tapit's owner, Ron Winchell. "He'd need to be 100 percent to run in this race and 110 percent to beat Smarty Jones. Michael didn't like the way he was going today. It wasn't right."

Dickinson could not be reached to comment.

The Cliff's Edge finished fifth behind Smarty Jones in the Kentucky Derby, but missed the Preakness with a bruised right front foot. The colt has recovered, but Zito said he and owner Robert LaPenta decided after yesterday's workout that a return for the Belmont would be too soon.

Despite the notable dropouts, new runners emerged for the $1 million Belmont this Saturday. Zito, already running Royal Assault, announced Birdstone would join the field after working six furlongs at Saratoga yesterday. Birdstone won the prestigious Champagne Stakes at Belmont last year as a 2-year-old, but has been a disappointment so far at 3, finishing eighth in the Kentucky Derby.

Purge, who scored a sensational victory in the Grade II $200,000 Peter Pan Stakes on May 22 at Belmont Park, is once again a possibility to run and could provide pace pressure for Smarty Jones in the 11/2-mile race.

Others scheduled to run are Preakness runner-up Rock Hard Ten; Eddington, who finished third; long shot Tap Dancer; and Caiman, winner of four of eight starts.

Racing Note: John Passero, widely hailed as perhaps the top track superintendent in the country, turned in a letter of resignation to the Maryland Jockey Club effective in 60 days. Passero has been in charge of maintaining Laurel Park and Pimlico since 1987. He also oversees the track surfaces at Colonial Downs.

Passero could not be reached to comment on his resignation, first reported in the Baltimore Sun.

Maryland Jockey Club President Joe De Francis and Chief Operating Officer Lou Raffetto declined to comment.

The Associated Press contributed to this report.