TOKYO -- Already reeling from a decline in popularity and a scarcity of young stars, Japan's ancient sport of sumo took another major hit Monday as Takanohana, one of its greatest wrestlers ever, announced he will retire.

The 6-foot-1, 330-pound wrestler, who was born Koji Hanada, told the Japan Sumo Association on Monday that he is quitting the sport.

''Initially, I had some mixed feelings about retiring, but I'm at peace with my decision,'' Takanohana said at a news conference. ''I'm very satisfied with what I have done in my career.''

Attesting to his phenomenal popularity, the news conference was televised live on all major networks. Even Prime Minister Junichiro Koizumi felt compelled to comment, calling the news ''regrettable.''

''He was a strong yokozuna whose victories were moving for many people,'' Koizumi told reporters.

The 30-year-old yokozuna, or grand champion, won 22 tournaments since his debut in 1988 -- the fourth best record in sumo history -- and had 701 victories and 216 defeats in the senior division.

Born to a sumo family, Takanohana was only 18 when he began competing in the elite makuuchi division, the youngest wrestler ever to do so. He steadily rose in the sport's rigid hierarchy, reaching the top rank in 1998. There have only been 67 yokozuna since the rank was created about 300 years ago. Takanohana's elder brother, Wakanohana, also a yokozuna, retired in March 2000.

Takanohana's departure is the third for a yokozuna in the past four years and comes at a particularly bleak period for sumo.

Attendance has dropped in recent years, as the sport's most celebrated stars have quit or been slowed by age and injury. At the same time, fewer youngsters have been willing to take on the rigorous sumo lifestyle, causing a dearth of promising, young talent.

Fans partly blame the sport's decline on its increasing emphasis on size, which has produced slower wrestlers who rely less on technique and are more injury-prone. The importance of bulk has also stoked rumors of performance-enhancing drug use -- though no cases have been proven -- and sumo officials are considering conducting doping tests for the first time ever.

Many wrestlers, who weigh as much as 180 kilograms (400 pounds), struggle with obesity, high blood pressure and diabetes as well as arthritic joints and chronic muscle pains during their careers and often well into retirement.

Takanohana was no exception.

After capturing four consecutive titles, Takanohana sat out his first tournament in 1996 with a back injury. He soon put on weight and his body began to betray him. He continued to win, albeit with less frequency, and the media focused on his injuries rather than his victories.

In May 2001, he tore ligaments in his knee on his way to winning his 22nd career title. That injury forced him to stay out of an unprecedented seven tournaments and fueled speculation about his retirement.

He appeared to be on the verge of a comeback last autumn, falling short of the championship only after losing to fellow yokozuna, Hawaii-born Musashimaru. But he then withdrew from the final tournament last year, complaining of knee trouble.

Takanohana returned to the ring for the tournament this month in Tokyo, but appeared sluggish and hurt his shoulder during a bout last Monday. A defeat Sunday was his final match.

Over his career, Takanohana's exploits inside the ring weren't the only source of his fame.

His breakup with his fiance, a famous actress, and a tiff with his brother several years ago were widely covered by the Japanese media. Angered by the publicity, he snubbed reporters, meeting their questions with a stony silence in the dressing room after bouts.

Takanohana's exit leaves Musashimaru as the sport's only active yokozuna. A Mongolian-born wrestler, Asashoryu, won the previous tournament and could be promoted to fill Takanohana's shoes if he can win the current one, which ends Sunday.

Other yokozuna, such as Hawaii-born Akebono, who quit in January 2001, often go on to head their own stables, the sport's traditional training grounds, where wrestlers are schooled in technique and strict etiquette.

Takanohana said he would help his father, Futagoyama, who runs his own stable. Futagoyama told the news conference he wants his son to succeed him at some point in the future.

In sumo, two wrestlers try to force each other down or out of an elevated clay ring. There are six sumo tournaments each year. Wrestlers face a different opponent on each of the tournaments' 15 days, and the one with the fewest defeats is declared the winner.

The sport traces its roots back more than a millennium to ancient religious ritual.