Representatives of the Salvadoran government's peace commission met today for the first time with leaders of the nation's left-wing opposition movement in the opening round of a dialogue aimed at achieving a negotiated settlement of the three-year-old Salvadoran civil war.

The two-hour meeting took place in Bogota, Colombia, news services reported. Here in San Salvador, President Reagan's special envoy for Central America, Richard Stone, expressed optimism for the peace process before he met with Salvadoran President Alvaro Magana.

"I feel optimistic. At least we are struggling together efficiently, seeking peace and justice," Stone told reporters before his talks with Magana. He arrived from Honduras, where he had met with government officials.

Stone, one of whose tasks is to arrange meetings between the Salvadoran government and the leftist opposition whose guerrillas are fighting to overthrow it, left later in the day for Costa Rica. He is on his fourth tour of the region since being named to his post in June.

Washington Post correspondent Loren Jenkins reported from San Jose, Costa Rica, that Stone is expected to meet Tuesday with a four-member Salvadoran leftist delegation that includes Ruben Zamora and Guillermo Manuel Ungo, leaders of the political umbrella organization called the Democratic Revolutionary Front.

The five armed groups fighting to overthrow the Salvadoran government have formed the Farabundo Marti National Liberation Front. This group is allied with the Revolutionary Front, a broad coalition whose leaders handle much of the diplomatic and political activity for the opposition.

Press reports from Bogota quoted Colombian President Belisario Betancur as saying that Stone was expected to arrive in Bogota Wednesday. It was in that city that Stone met Zamora on July 31.

In Bogota, one of the opposition representatives called today's meeting "historic," while the peace commission's leader said the talks were "important for our future and that of Central America."

But the two sides begin the discussions with widely divergent positions on what subjects are to be considered, and it is unclear whether substantial progress will be possible.

The Salvadoran government, with strong backing from the United States, insists that the talks should deal only with setting terms for the leftist opposition to participate in elections early next year. The opposition, instead, wants to discuss forming a provisional government, including their own representatives, that would then set up elections.

The meeting in Bogota today was between peace commission members Francisco Quinonez and Bishop Marco Rene Revelo, and opposition representatives Oscar Bonilla and Carlos Molina, also members of the political coalition. Colombian President Betancur, who is playing a leading role in encouraging negotiations in the Salvadoran conflict, also participated, according to press reports from Bogota.

The parties did not say afterward specifically what was discussed at the meeting, although Betancur said additional meetings were possible.

Bonilla said before the meeting that the opposition's goal was "to find agreement on the points for a later meeting between both parties."

The three-man peace commission was established in February to seek initial talks with the opposition without directly involving government leaders.

The government is under pressure from conservative critics to defeat the guerrillas on the battlefield rather than seek a negotiated solution.

After the meeting in Bogota, commission leader Quinonez reiterated that the government's aim is to draw the leftist opposition into the electoral process.

"The government agreed to converse with the guerrillas because it represents millions of Salvadorans who want peace," Quinonez, an industrialist, was quoted as saying in news agency reports from Bogota.

"There are a few who don't want peace, and thus it is necessary to incorporate them in the democratic process that is alive in the country, which will culminate with the presidential elections planned during the first trimester of next year."

However, the guerrilla front and its civilian allies issued a statement over the weekend again rejecting participation in the planned elections and blaming the United States for the continuing conflict in El Salvador.