Mikhail Tal, a Latvian grandmaster who held the world chess championship in 1960-61 and was one of the game's most popular and exciting players, died in Moscow yesterday after a long illness, the Russian news agency Itar-Tass reported. He was 55 years old.

Since the breakup of the Soviet Union, Mr. Tal had hoped to represent Latvia in this month's world chess Olympiad in Manila, but was unable to make the trip because of illness. No cause of death was given, but he had suffered from liver and kidney ailments for many years. Itar-Tass said he died after being taken to a hospital to undergo surgery for a severe kidney illness.

Known in chess circles as a swashbuckling attacker who reveled in daring sacrifices and all-but-unfathomable complications over the board, Mr. Tal won the world championship in 1960 at the age of 23 -- becoming the youngest person to hold the title in this century -- by defeating Mikhail Botvinnik, who had been the champion since 1948.

Although Mr. Tal lost the championship in a return match with Mr. Botvinnik a year later and never became a title challenger again, he continued to play at world-class levels of competition and steadily won tournament and brilliancy prizes in an illustrious chess career.

While his slashing style earned him the sobriquet "Tal the Terrible," friends called him Misha, and he was known in the chess fraternity as one of the game's most popular and amiable figures: a gentle, witty man who seemed totally immersed in chess and displayed none of the egotism that is common among top-level contenders.

Because of his nearly lifelong struggle with liver and kidney ailments, friends recalled last night, it was not unusual for Mr. Tal to be hospitalized during tournaments. But he was so keen to continue that he often returned to the action and occasionally played tournament or match games at his hospital bed, as he did once in the early 1960's with Bobby Fischer, the American who would later become world champion.

Mikhail Tal was born on Nov. 9, 1936, and was taught to play chess at the age of 6 by his father, a doctor in the Latvian village of Yurla, near Perm. Though he had an astonishing memory and was so eager for knowledge that he was placed in the fourth grade in his first year of school, the youngster showed little interest or talent for chess at first, preferring books and more active pastimes.

But playing with a cousin a few years later sparked a new and absorbing interest in the game, and the boy joined the chess club of the Palace of Young Pioneers in Riga, the Latvian capital. He began playing in tournaments and steadily improved under an able tutor, Aleksandr Koblents.

At the age of 16, Mr. Tal's play earned him the rank of national master and three years later, in 1957, the year he graduated from Riga University with degrees in history and philosophy, he became a grandmaster, joining the select ranks of the world's best players.

He soon was beating those players regularly and, in 1960, crushed Mr. Botvinnik for the world championship by a score of 12 1/2 to 8 1/2, astounding the chess world. Mr. Botvinnik had held the championship for 12 years in one of the longest reigns in the game's history, and the intense young Latvian challenger was virtually unknown outside chess circles.

Mr. Tal swept the champion away with his characteristic flare for the dramatic -- a series of sudden, entirely risky moves that turned the games into inextricably complex positions. Months of analysis later proved many of these moves to be unsound, but his opponent was unable to solve them over the board.

In the return match in 1961, experts said, Mr. Botvinnik managed to avoid Mr. Tal's diabolical complications by steering the play into end games that gave him an advantage.

In succeeding decades, Mr. Tal continued to play at exceptionally high grandmaster levels, despite his frail health. At the board, he often stared fixedly at opponents, a habit that disconcerted many and even led some to accuse him of trying to hypnotize them.

But, experts said, it was his capacity to envision combinations and deeply analyze complex variations -- not hypnosis -- that made him formidable over the board.

"He had an insatiable appetite for the game," Robert Byrne, an American grandmaster who is The New York Times chess columnist, said of Mr. Tal last night. "It sounds trite, but few love the game as much as he did. You could just see it. Some players consider it labor. This man loved chess."