20,000 Rally to Protect Lithuania’s Parliament : Baltic unrest: Nationalists block pro-Moscow marchers. Deployment of Soviet troops near confrontation raises tensions.

Soviet troops and armored vehicles were deployed in the Lithuanian capital of Vilnius on Wednesday as thousands of demonstrators opposing and supporting the republic’s struggle for independence from the Soviet Union confronted one another across a square in the city’s center.

An estimated 8,000 pro-Moscow demonstrators, demanding that President Mikhail S. Gorbachev remove Lithuania’s nationalist government and rule the republic himself, had planned another march on the Parliament building, which they had tried to storm on Tuesday.

But they were blocked by about 20,000 Lithuanian nationalists who had responded to a call by Vytautas Landsbergis, the republic’s president, to protect the Parliament, according to journalists at the scene. A triple line of police officers separated the two groups.

Tensions rose sharply in mid-afternoon when a company of troops from the Soviet Interior Ministry, supported by armored personnel carriers, took up positions near the Parliament building.

Lithuanian officials feared they would intervene on the side of the pro-Moscow demonstrators, mostly Russians and Poles, and perhaps occupy the Parliament building themselves in the guise of protecting it.

As supporters of Landsbergis’ nationalist government continued to stream toward the center of the city, the potential grew for a major clash and what one deputy said would be “a political explosion . . . that would shake every capital around the world.”

With the deployment this week of paratroops to the Baltic republics of Lithuania, Latvia and Estonia to round up draft evaders and military deserters, nationalist leaders see Gorbachev yielding to mounting pressure from the right, particularly the Soviet military, to crack down on independence movements.

In Vilnius, a major clash appeared imminent for a time Wednesday afternoon as the crowds of pro-Moscow and nationalist demonstrators, waving banners and hurling insults at one another, grew rapidly and threatened to burst the police lines.

But Landsbergis then made a dramatic appeal to the crowd to remain calm and avoid any actions that might be taken as provocations as even more nationalist supporters streamed to the scene.

“Please believe in us as we believe in you--please keep calm,” Landsbergis said, according to the Lithuanian news agency ELTA. “Parliament is working. Your deputies are working. We are now discussing the question of reorganizing the government. Please, please remain calm.”

Parliament was debating the formation of a new government for Lithuania in the wake of the resignation Tuesday of Prime Minister Kazimiera Prunskiene and her Cabinet in twin disputes over economic reforms--particularly increased food prices--and her moderate approach to negotiations on the republic’s secession from the Soviet Union.

Deputies from the pro-Moscow faction of the Communist Party demanded that the Supreme Council, the republic’s Parliament, be dissolved and new elections be called--or that Lithuania be placed under presidential rule.

“This Parliament has no moral right to continue its work,” Vladislav Shved, a Communist Party leader, declared.

More military units, both from the internal security forces and the Soviet army, were deployed, meanwhile, at the radio and television transmission tower and the republic’s main printing plant, and the government’s information bureau reported that two planeloads of paratroopers, accompanied by armored vehicles, landed at the city’s airport.

Landsbergis continued to caution Lithuanians not to respond with violence to the growing military presence throughout the republic.

The tense confrontation ended at nightfall, when the pro-Moscow demonstrators dispersed and the nationalists shrank to a few hundred who volunteered to protect the Parliament overnight. The internal security troops and paratroopers returned to military bases around the city. No violence was reported.

Lt. Gen. Franz Markovsky, a top official of the Soviet general staff, later denied suggestions by Lithuanian and other Baltic leaders that the armed forces were planning to seize power there or in other republics seeking independence from Moscow.

“The military command has never planned and is not planning a military coup on any of the republics of the Soviet Union,” Markovsky declared on Soviet television in response to widespread speculation about the deployment of paratroopers to round up draft evaders and military deserters in seven regions around the country.

With only 12% of Lithuanian draftees reporting for military service--the proportion is 25% in Latvia, 24% in Estonia and only 10% in the southern republic of Georgia--the Soviet military sees not only its ranks in danger of depletion but the authority of the central government challenged on fundamental issues.

Conservatives, whose influence is growing, bluntly told Gorbachev last month at the Congress of People’s Deputies, the national Parliament, that, unless he can halt the separatist trends around the country, the Soviet Union will be threatened with dismemberment. Gorbachev responded with a renewed commitment to maintain the state’s integrity.

In Moscow, 16 representatives from pro-Moscow groups met with Rafik Nishanov, chairman of the Soviet legislature’s Council of Nationalities, to demand that the Kremlin remove the Landsbergis government and rule the republic directly.

Boris N. Yeltsin, the president of the Russian Federation, largest of the Soviet Union’s constituent republics, warned the central government against any use of force to suppress the independence-minded nationalist movements, which now control Estonia, Latvia and Lithuania; Armenia and Georgia in the south, and Moldova on the border with Romania.

In the southern Soviet republic of Azerbaijan, three soldiers and a journalist were shot to death Wednesday in an ambush by members of an Armenian militia in the disputed Armenian enclave of Nagorno-Karabakh, the Soviet news agency Tass reported.