Gorbachev Warns Lithuania: Back Down or Face Blockade : Secession: His ultimatum gives the republic two days to rescind its independence moves or face a cutoff of oil and other vital goods.

Soviet President Mikhail S. Gorbachev on Friday threatened the toughest action yet to quash Lithuania’s month-old independence bid: an economic blockade of oil and other vital products if the breakaway Baltic republic does not reverse its challenge to Moscow’s rule within two days.

Affairs are now at a “political dead end,” Gorbachev and Prime Minister Nikolai I. Ryzhkov said in a toughly worded letter to the Lithuanian leadership. The letter, distributed by the official news agency Tass, betrayed the Kremlin’s worry over the effects of Lithuania’s continuing defiance of Moscow, including the danger of pro-independence contagion spreading to other regions.

Vytautas Landsbergis, Lithuania’s president, called the ultimatum a bitter “Easter gift” designed to sap support for his government in the republic by sparking unemployment and wreaking economic disorder.

But Landsbergis said in Vilnius, the Lithuanian capital, that his republic would not give in. He predicted that the Soviet economy, highly interconnected after more than 70 years of centralized state management, would suffer as a whole from any harm done to one of its parts.

Meanwhile, the British news agency Reuters reported from Moscow that Soviet soldiers had burst into the institute of Communist Party history in Vilnius on Friday and expelled pro-independence volunteers guarding its sensitive archives. The institute’s director, Vanda Kasauskiene, said about 20 soldiers occupied the building, which has been at the center of a dispute between the rival pro-Moscow and independent Lithuanian Communist parties for weeks.

The archives are believed to contain material relating to the republic’s forcible incorporation into the Soviet Union in 1940. Lithuanian nationalists fear it might be removed.

In their letter, Gorbachev and Ryzhkov declared that the Baltic republic “continues to adopt legislative acts and decisions that set Lithuania in opposition to other republics and the Soviet Union as a whole.”

Such actions, they wrote, “aim to undermine political and socioeconomic stability in the country, damage democratic processes and seriously infringe on Soviet citizens’ rights.”

They objected specifically to the decision by the Supreme Council, Lithuania’s Parliament, to halt the spring call-up of young men for conscription into the Soviet armed forces, a “flagrant violation of the U.S.S.R. Law on General Military Service.”

Likewise, Gorbachev and Ryzhkov said Lithuanian authorities are making “illegitimate attempts” to seize property rightfully belonging to the Soviet Communist Party, and discriminating against law-abiding Soviet citizens by adopting a law on issuing identity cards to citizens of a “Lithuanian Republic.”

“Such actions, the list of which continues, can no longer be tolerated,” the Kremlin leaders said.

“In this situation, we are compelled to issue the following warning: If the Supreme Soviet and the Council of Ministers of the Lithuanian S.S.R. (Soviet Socialist Republic) do not rescind the above decisions within the next two days, instructions will be given to stop supplies to the Lithuanian S.S.R. from other constituent republics of those categories of products that are sold on external markets for freely convertible currency.”

Oil and natural gas make up the bulk of Soviet exports sold abroad for dollars and other so-called hard currencies, but the broad phrasing used by Gorbachev and Ryzhkov indicated that shipments of any marketable Soviet export, from caviar and gold to Lada cars and Stolichnaya vodka, could conceivably be included.

Moscow authorities have already ordered that privately held firearms be surrendered in Lithuania, deployed soldiers to seize army deserters and staged displays of military might, apparently to cow the population into submission. But an economic blockade would have a far wider impact on the lives of the 3.7 million inhabitants.

Landsbergis, speaking to reporters in his offices in the Supreme Council building in Vilnius, expressed surprise at the timing of Gorbachev’s ultimatum but not at the possibility of a Soviet blockade of his homeland, which has ports on the Baltic Sea but an international frontier with only one country, Poland.

“We were not waiting for such a letter this weekend,” Landsbergis said. “We had expected it, but not on Easter--an Easter gift for us.” He said his countrymen would respond by defying the two-day time limit set by Gorbachev.

“There are two reasons why we can’t do this. One, because they are our state decrees, and we won’t change our decision. The second is that we are not working on Easter,” said Landsbergis, who is also chairman of the Sajudis People’s Front organization that waged a two-year grass-roots campaign for restoration of this largely Roman Catholic land’s sovereignty.

What would happen in the event of a blockade is unclear. Lithuania is relatively resource-poor, with deposits of peat, gypsum, limestone, marl and dolomite but no appreciable source of natural gas or petroleum. It does, however, boast one of the Soviet Union’s most efficient agro-industrial complexes.

Landsbergis said he had previously received “propositions” from unidentified Scandinavian countries to supply oil via the Baltic port of Klaipeda, but gave no details.

It was also unclear whether the Kremlin would allow such resupply by sea.

“If Moscow will close our ports with military ships, it will be quite a performance for all the world,” Landsbergis said. He said Moscow’s warning would only accelerate moves by Lithuania and the other two Baltic republics, Latvia and Estonia, to form an integrated economy freed from the central government’s grip.

The prime ministers of Lithuania, Latvia and Estonia signed a “Baltic Common Market Agreement” pledging increased political and economic cooperation on Thursday.

Aurimas Drizus, a Sajudis official, said the Lithuanian economy has already been subjected to the Kremlin’s anger; for example, he said, a Kaunas factory that manufactures parts for Soviet-made radios and televisions has not received any orders from the rest of the country since February.

The Lithuanians have said they are ready to negotiate anything with Moscow, except the Parliament’s declaration of March 11 proclaiming a re-establishment of the independence that their homeland enjoyed between the world wars. All three republics were forcibly absorbed by the Soviets in 1940.

Gorbachev and Ryzhkov, however, kept to Moscow’s previous line that there can be no negotiations as long as the independence proclamation that the Soviet Congress of People’s Deputies ruled illegal and invalid is still in effect.

“We look to the Lithuanian Supreme Soviet and the Council of Ministers to take decisions that will restore the republic’s position to that of March 10, 1990,” the Soviet leaders said. “This would make it possible to deal with the entire package of issues without delay.”

Justifying an economic blockade, Gorbachev and Ryzhkov said it makes no sense for the rest of the country to keep supplying a republic that now refuses to play its assigned role in the national economy.

Esther Schrader, a free-lance journalist in Vilnius, contributed to this report.