MOSCOW (AP) _ Soviet authorities began pumping natural gas to a fertilizer plant in Lithuania today, easing the blockade on fuel supplies to the breakaway Baltic republic.

In neighboring Latvia, leaders of pro-independence fronts from all three Baltic republics gathered at a resort near the capital, Riga, to discuss the future of their secessionist movements.

Officials in Latvia and Lithuania also met separately to discuss compromises offered by Soviet President Mikhail S. Gorbachev in an effort to get talks started between the republics and the Kremlin.

The Baltic republics of Lithuania, Latvia and Estonia were annexed by the Soviet Union 50 years ago. They have all been seeking more autonomy, but Lithuania has been the only one of the three to declare independence.

A spokesman for the Lithuanian parliament, Aidas Palubinskas, said he was told today by a pipeline dispatcher that natural gas was again flowing from the Soviet Union to the Azotas fertilizer plant in the city of Jonova.

The move fulfilled a promise made to Lithuanian Prime Minister Kazimiera Prunskiene on Wednesday by Soviet Prime Minister Nikolai Ryzhkov that 15 percent of the republic's daily natural gas supply would be restored.

Politburo member Yuri D. Maslyukov told a news conference in Moscow on Friday that the restoration of fuel to the Lithuanian plant was a goodwill gesture from the Kremlin and a ''reiteration of the Soviet government's interest in speeding negotiations.''

More than 26,000 people have been thrown out of work in Lithuania due to the Kremlin's blockade of all oil, most natural gas and some raw materials.

Gorbachev imposed the embargo after the republic refused to rescind its March 11 declaration of independence.

Palubinskas said that restoration of gas supplies to the Azotas plant would mean that 1,600 laid-off workers - out of a staff of 4,500 - should be back at work by the end of next week.

At the beachfront resort of Jurmala in Latvia, leaders of the popular fronts of Latvia and Estonia and the Sajudis movement of Lithuania opened the second Baltic Assembly.

''The participants are assessing their movements' role in conditions where the fronts' representatives won a majority in republic parliaments and local councils,'' the Soviet news agency Tass said.

Tass said the delegates, 50 from each of the pro-independence movements, also discussed cooperation between the Baltics and other Soviet republics.

Speakers at the one-day assembly concluded that prospects for achieving full independence have grown dramatically over the past year. They cited the introduction of democratic governments in Eastern Europe and the reshaping of the Warsaw Pact into a political alliance, said journalist Alexander Sidyachko, who attended the meeting.

He said they adopted a resolution calling on the 35 signatory nations of the Helsinki Accords to hold a conference on the Baltic drive for independence.

The first Baltic Assembly was held in the Estonian capital, Tallinn, in May of last year.

In Lithuania, Mrs. Prunskiene and her top ministers discussed a proposal by Gorbachev, who offered to open talks if implementation of the republic's independence declaration was frozen, the unofficial Interfax news agency said.

The proposal will be discussed by a full session of the Supreme Council next week, Lithuanian President Vytautas Landsbergis was reported as saying at the Baltic Assembly.

Latvian ministers also discussed proposals by Gorbachev aimed at leading toward negotiation on their calls for independence.

The Latvian leadership concluded that Gorbachev was not specific enough in his compromise offer, Sidyachko said by telephone from Riga. However, he quoted legislator Andrei Pantaleyev as saying an official response to Gorbachev could only be issued by a full meeting of the republic's Supreme Council.