Thousands in Lithuania Demand Independence : East Bloc: The demonstration comes a day before Gorbachev visits the Baltic republic.

Thousands of Lithuanians, carrying national flags and banners, rallied to demand independence from the Soviet Union today, a day before Mikhail S. Gorbachev’s scheduled trip to confront the Baltic republic’s defiant Communist Party.

A sea of banners, posters and yellow, green and red vertically striped Lithuanian national flags filled historic Cathedral Square in the medieval city as about 25,000 people gathered to demand an end to half a century of Soviet rule.

Banners carried by demonstrators ranged from one polite welcome to more blunt calls for Gorbachev to go home and take the Soviet army with him.

“We didn’t join the Soviet Union, you grabbed us!” read one banner, referring to the Soviet Union’s annexation of the Baltic republic in 1940.

Gorbachev is expected Thursday for three days of meetings with factory workers, collective farmers, members of ethnic minorities and Communist Party activists to try to reverse the Lithuanian Communist Party’s decision Dec. 20 to split from the national party and support independence for the republic.

It was the first such break since the Communists took power in Moscow in 1917. The Soviet leader has consistently and sharply criticized Lithuanian Communist leaders for the move for independence.

Leaders of Sajudis, a grass-roots Lithuanian political movement, hope to draw 1 million of Lithuania’s 3.7 million people to Vilnius on Thursday to show Gorbachev the extent of support for independence.

A spokesman for Sajudis, Rimantas Kanapienis, said the organization rejected a call by Kremlin ideology chief Vadim A. Medvedev, sent to Lithuania in advance of Gorbachev’s visit, to call off the rally today.

Medvedev indicated Tuesday that the Moscow leadership favors granting Lithuanians more autonomy as part of the union but remains opposed to Lithuanian secession.

Demonstrators, waving the Lithuanian flag, made it clear today they believed that it is too late for Gorbachev to change the course for independence.

“Lithuania has already decided,” one sign said.

Lithuania was recognized as an independent country by Soviet founder V. I. Lenin, but Josef Stalin annexed it in 1940 as part of a secret Nazi-Soviet treaty.

One sign read: “Lenin recognized Lithuania. Stalin took away its independence, and Gorbachev?”

Gorbachev last visited one of the Baltic republics in February, 1987, when he traveled to Riga, Latvia.

Activists in Lithuania, which was absorbed by the Soviet Union along with the other Baltic republics of Latvia and Estonia, have been approaching the call for independence for 18 months.