Bolivia's first democratically elected government in more than a decade was overthrown today when troops led by Army Col. Alberto Natusch Busch seized the presidential palace here, closed down the airport, surrounded President Walter Guevara Arze's home and announced that Natusch would form a new military government.

There was sporadic resistance to the troops once they took positions throughout this capital. Six persons, mostly students, were reported killed and eight others wounded.

The coup came omly eight days after U.S. Scretary of State Cyrus Vance held a luncheon in the U.S. Embassy here for Bolivia's top civilian and military leaders, warning them that the United States would look with utmost disfavor if the democratic government, less than three months old, was toppled.

Since the military initiated a return to representative rule last year, the Carter administration has made repeated statements of support and cited Bolivia as a leader in a Latin American trend that President Carter has encouraged.

[In Washington, State Department spokesman Thomas Reston said the United States deplores "any disruption in Bolivia's democratic process. We will be reviewing our relations with Bolivia as events develop."]

Vance was in La Paz for the opening of the General Assembly of the Organization of American States, which ended last night about six hours before the coup began.

Bolivia's largest labor federation began a 24-hour general strike to protest the coup.Guevara escaped from his home and went into hiding, and the country's major political parties denounced the new government.

At a press conference shortly after assuming the presidency, Natusch said his plan was to allow the recently elected congress to continue functioning, respect the unions and political parties, form a new Cabinet composed mostly of civilians and call elections after a short period of military rule.

Several diplomatic observers here said they thought Natusch would have to impose a very harsh military dictatorship over this Andean nation of 5 million people because he seemed to have little popular or political support.

Natusch was still attempting to form a cabinet tonight after several ministers named earlier in the day announced they would not join his new government.

Although La Paz seemed calm this afternoon after many machine gun encounters this morning, troops and tanks were still in place around all major government buildings and the politically volatile university.

The congress was allowed to meet about 8 p.m. and passed a resolution condeming the coup and calling for a restoration of a constitutional government.

Gen. David Padilla, the last military president and the current armed forces chief of staff, denounced Natusch and the troops supporting him as "a subversive group." He warned that if they did not lay down their arms and return the government to Guevara they would have to accept the "consequences"

Natusch, 52, accused Padilla of wanting "to bloody the nation and divide the armed forces."

Guevara and his Cabinet met in hiding with a few journalists to announce their determination to resist the military takeover.

Saying "this is sad day for all Bolivians," Guervara warned that the coup could lead to civil war.He pleaded with those in the military who remained loyal to the democratic government to "exhort their comrades to put down their arms to avoid a bloodbath between brothers."

But cities throughout Bolivia were reported calm and Gen. Juliop Herrara, only member of his Cabinet not to go underground, said that "not one unit in the country" has failed to support the new government.

Bolivia has been in an almost continuous political crisis since Guevara became interim president Aug. 10. He was named by the newly elected congress when neither of the country's two most important political figures, former president Victor Paz Estenssoro and Hernan Siles Zuazo, obtained enough votes in the general election to be elected outright or to obtain a majority in the congress.

The coup -- Bolivia's third in the past 16 months -- was widely rumored during the past week. Almost everyone here knew that Natusch, who refused to attend Vance's lunch, was plotting with dissident members of both Paz's and Siles' coalitions.

But the U.S. Embassy here indicated optimism as late as yesterday that Guevara would fashion a coalition Cabinet that might forestall the coup and end the political paralysis that had developed between Guevara's government and the congress, which was controlled by Paz and Siles.

There appeared to be widespread sorrow and anger here that the Guevara government was deposed. Early this morning citizens were seen and heard in the streets yelling to no one in particular. "This is a tragedy. The military has returned."