Lithuanian Demonstration Blocked : Soviet Union: KGB guards prevent 20,000 from making a symbolic border crossing. Armenia and Turkmenia take steps toward independence.

More than 20,000 Lithuanians flocked to the Polish border Thursday in a dramatic reminder to the world and the Kremlin that they are determined to be independent, but KGB guards thwarted their plans to take symbolic control of the border by crossing it en masse.

In Armenia, 1,500 miles to the south, the republic’s legislature approved a declaration of independence that stopped short of immediate secession but claimed the right to have an independent army and foreign policy and a separate currency.

In still another example of what appears to be the accelerating breakup of the Soviet Union, the Central Asian republic of Turkmenia declared its sovereignty, the 12th of the 15 republics to enact legislation demanding that Moscow allow it more control over its affairs.

President Mikhail S. Gorbachev, who is struggling to hold the country together with promises of better economic reforms and a new treaty of unity, said that government economists had made “enormous progress” and would soon have a program ready.

“We’re on the threshold of big decisions,” Gorbachev said in a 15-minute talk on national television.

But he also issued a decree that highlighted the growing conflict between the Kremlin and the Russian republic, which is headed by the radical populist Boris N. Yeltsin.

The decree declared that the Russian republic’s claims to full control over the sale of its oil, gold and other resources were invalid.

Russian officials had warned the central government that they would review foreign contracts signed by the Kremlin--including a $1-billion diamond deal with the South African firm of De Beers Consolidated Mines Ltd. They recently backed away, saying the contracts will be honored, but are still pushing for exclusive control of all minerals in the republic, which accounts for two-thirds of the Soviet Union’s land.

Delegates from Estonia brought the tiny Baltic republic’s claims to statehood to the bargaining table Thursday, making theirs the first republic to open formal negotiations on independence with the Kremlin. The other two Baltic republics--Lithuania, which declared its independence on March 11, and Latvia--also are fielding negotiating teams.

On the Soviet-Polish border, a three-day event organized by Lithuanians peaked Thursday on the 51st anniversary of the Soviet pact with Nazi Germany that led to the Soviet annexation of the three Baltic states.

Members of Sajudis, the Lithuanian popular front, had planned a mass crossing into Poland to demonstrate their desire to open Lithuania to the rest of Europe, but officials refused to allow them passage, and more than 1,000 soldiers, backed up by armored personnel carriers, kept them at bay. No violence was reported.

Lithuanian President Vytautas Landsbergis, standing among demonstrators at the border, emphasized the symbolism of the gathering.

“This action,” he said, “will allow the destruction of one of the old Bolshevik myths, that once the Soviet Union has seized territory, then it is sacred Soviet territory, and that crossing the line, even passing the barrier, is the most abominable thing.”

Small groups of Soviet and Polish citizens were allowed to cross the border. About 150 Poles, many of Lithuanian heritage, crossed at noon, after more than 500 Lithuanians had visited the Polish side on Wednesday.

“I came to show the Lithuanians that we are in solidarity with them,” Petras Voiznelia, an 18-year-old Pole, told a reporter.

Lithuanians, who had put up a colorful tent city near the border to protect themselves from the rain, pressed against a barbed-wire fence as the Poles came across.

“We want to be free,” Albina Spakauskene, 62, said. “I feel terrible pressed here against this fence. It’s obvious we’re still in a concentration camp.”

In neighboring Latvia and Estonia, residents lit bonfires to commemorate the signing of the Molotov-Ribbentrop pact, the 1939 agreement between Moscow and Berlin.

In Armenia, the lawmakers voted 183 to 2 in favor of the declaration of independence to which they had agreed in principle on Tuesday. The document rejects the Communist-inspired name Armenian Soviet Socialist Republic and replaces it with Republic of Armenia.

The declaration claims local control over laws, taxation, the banking system and customs, and gives Armenians living abroad the right to citizenship in the Armenian republic.

The document empowers the Armenian government to create its own armed forces, “with the goal of guaranteeing the security of the Republic of Armenia and the inviolability of its borders.”

Thousands of Armenians have already joined groups of militants sworn to defend the republic in its virtual civil war with neighboring Azerbaijan. Armenia’s new president, Levon Ter-Petrosian, has promised Moscow officials that he will bring the militants under control, but armed clashes in the border region between the two republics have flared repeatedly this week, leaving at least 50 reported dead.

The Armenian declaration asserts that Nagorno-Karabakh, the autonomous region that is at the center of the dispute between Armenia and Azerbaijan, should be reunited with Armenia, and this seemed likely to add fuel to the conflict.

Shogren reported from Lazdijai and Goldberg from Moscow.