VILNIUS, USSR--President Mikhail S. Gorbachev assured independence-seeking Lithuanians yesterday that they would have a say in their republic's future, but he cautioned that a confrontation with Moscow could lead to "tragedy."

An estimated 300,000 Lithuanians defied the visiting Gorbachev by jamming central Vilnius yesterday evening in a candlelight demonstration for freedom.

"We have been tied together for these 50 years, whether we like it or not," Gorbachev told a crowd earlier in the day after placing a wreath at a monument to Vladimir Lenin.

Gorbachev said later that he has ordered that a law be written and published establishing a mechanism for secession from the Soviet Union, a right guaranteed by the country's 1977 constitution but not recognized to date.

"I am for self-determination all the way to secession from the Soviet Union", Gorbachev told a meeting of Lithuanian intellectuals. Gorbachev appeared to be saying that although he vigorously opposes such a move, he understands it could be a possibility.

"Sovereignty is a natural desire, but in the framework of a federation," Gorbachev said, according to Lithuanian TV correspondent Eduardas Potesinskas.

It was not clear how independent Lithuania would be under the unspecified framework that Gorbachev envisioned.

Lithuanians say they want to restore the independence they had between the world wars. Soviet dictator Josef Stalin absorbed Lithuania along with the two other Baltic states, Latvia and Estonia, in 1940 under a secret agreement with Nazi Germany.

Although he has granted Lithuanians and their neighbors in Latvia and Estonia a large measure of economic and political power, Gorbachev has consistently and sharply criticized Lithuanian Communist Party leaders for pressing for complete independence.

He convened an emergency session of the national party's Central Committee last month to discuss the issue.

By going to Vilnius, Lithuania's capital, Gorbachev put his personal prestige on the line as never before in his nearly five years in power, appearing in a republic that openly disagrees with him and is unlikely to be moved by his appeals.

Gorbachev is in Lithuania for three days of meetings to try to reverse the Lithuanian party's break with the national party, decided in December.

Gorbachev waded into a crowd of several hundred people in Vilnius after the visit to the Lenin monument, and he talked for nearly an hour.

One man in the crowd called out: "People must decide their own fate!"

"Nothing will be decided without you," Gorbachev replied. "We will decide everything together."