NEW YORK (AP) _ Dan O'Brien, the world record-holder in the heptathlon, and Suzy Hamilton, the national champion in the women's 1,500 meters, were among the missing today when the U.S. track and field team left for the World Indoor Championships in Japan.

O'Brien did not go because he is not ready to compete against the world's best, while Hamilton has been bothered by a left Achilles injury.

Overall, the Americans sent a 46-member team _ 24 men and 22 women _ to Maebashi, Japan, for the three-day championships, beginning Friday.

Each country was allowed a maximum of two participants, by qualification, in each individual event, except for the multi-events _ the heptathlon for men, the pentathlon for women. Those were by invitation from the International Amateur Athletic Federation, the world governing body.

The multi-event invitations were based on last year's world outdoor rankings in the men's decathlon and women's heptathlon. On that basis, O'Brien, the world's top-ranked decathlete, was invited.

He declined because ``we don't think he's ready to compete at that level at this time,'' his coach, Rick Sloan, said Monday.

``We don't compete if we don't feel he's ready mentally and physically to dominate the competition and set a world record,'' Sloan said.

``We'll be ready for them outdoors.''

O'Brien competed in the 1993 indoor championships and set the world record of 6,476 points.

He also is the world record-holder in the decathlon with 8,891 points, the 1996 Olympic gold medalist and a three-time world outdoor champion.

O'Brien's absence left Chris Huffins as the only American in the heptathlon.

Hamilton, one of the world's premier middle-distance runners and a two-time Olympian, had been hurt two weeks before winning at Saturday's USA Championships at Atlanta.

Her absence left the U.S. with only one woman in the 1,500, Alisa Harvey. The women also had only one competitor in the 3,000, high jump and pentathlon, and none in the triple jump, because none qualified.

The men also were one short in the 800, high jump and triple jump.