President Tito's doctors amputated his left leg this afternoon after convincing the 87-year-old Yugoslav leader that the surgery was absolutely necessary to save his life.

A medical bulletin tonight said that Tito had "taken the operation well" and that "his condition was normal in the immediate postoperative period."

Medical sources here interpreted the official bulletin as suggesting that the Yugoslav leader was out of immediate danger. But they cautioned that possible complications could develop in view of his advanced age and the fact that he had undergone long and unsuccessful surgery a week earlier.

The state of Tito's health has generated widespread concern in Europe because it raises the prospect of the first trnasition of power in 36 years in this independent communist country, which he took out of the Soviet Bloc in 1948. It comes at a time when the Soviets are pursuing a more assertive course in international affairs that has prompted fears here that they may seek to reincorporate Yugoslavia in the bloc.

As they were gearing up for the transition, authoritative Yugoslav spokesmen have publicly stated in recent days that the Kremlin has taken over two countries -- directly on by proxy -- in the past 12 months and that Yugoslavia has no intention of becoming another Afghanistan or Cambodia.

Despite his advanced age, Tito has remained a shrewd and skillful diplomat who kept his country within Moscow's reach but beyond its grasp. At the same time he has maintained close ties with nonaligned countries and friendly relations with most Western nations. His successors may have a more difficult task in steering that course.

Yugoslav sources said tonight that Tito had resisted amputation until this morning when he was told by the eight-man team of physicians that there was no other way. "Get on with your job," he was reported to have said.

The medical bulletin issued by the official Tanjug news agnecy said his "left leg was amputated because of severe damage to the arteries which had blocked the circulation and speeded up devitalization of the tissue to endanger his life."

Tanjug did not say how much of the leg had been amputated, nor did it mention other details of his condition, such as his temperature and blood pressure.

Tito underwent surgery on the night of Jan. 12, when doctors at a clinic in Ljubljana, the Slovenian regional capital, attempted to remove a circulatory blockage. After an initially optimistic bulletin at that time, the doctors conceded two days later that their bypass surgery had failed. The subsequent communiques spoke about "gradual deterioration" of his leg.

There was some confusion as to when the second operation was performed. Well-informed Yugoslav sources insisted earlier that Tito underwent major surgery last night, following the announcement yesterday that a second operation would be necessary, although tonight's official bulletin said the operation was this afternoon.

Terse medical information, however, is in line with Yugoslavia's general state of alertness since Tito's hospitalization. This includes a state of military preparedness of both the armed forces and the General People's Defense, a paramilitary organization of more than a million men.

The government has also issued warnings against any foreign interference in Yugoslav affairs while also assailing Bulgaria, Moscow's most loyal ally, for haboring territorial claims against Yugoslavia.

For all the flurry of speculation about possible Soviet interference in Yugoslavia, diplomatic sources here do not foresee any overt Soviet action. But they believe that Moscow is preparing to exploit existing divisions within this multinational country.

Yugoslavia was created at the end of World War I from several south Slavic nations and was torn in bloody civil strife in World War II. Tito has been viewed by Yugoslavs as a leader who imposed a considerable degree of cohesion on the quarreling nationalities and is regarded as a lynchpin in the system he created.