U.S. Ambassador Paul H. Boecker recommended to the State Department yesterday that the United States cut off economic and military aid to Bolivia unless the new government here agrees to hold another round of elections within six months, according to well informed sources.

Boecker's recommendation, if accepted in Washington, could mean cancellation of $78 million in pending aid requests and would constitute a tough response to last Friday's coup, which saw Juan Pereda Asbun emerge as president after toppling the 7-year-old military government of Gen. Hugo Banzer.

[State Department spokesman Hodding Carter III said, "we deeply regret developments in Bolivia" and are "withholding any judgments" on recognition pending clarification of the new ruler's intentions. He said the United States hopes for prompt moves fulfilling "the legitimate aspirations of the Bolivian people."]

Pereda, who had been the Banzer government's official candidate for president in Bolivia's first elections in 12 years, asked last Wednesday that the July 9 election results be annulled and that another election be held before the end of the year because of widespread allegations of fraud in Pereda's behalf.

According to informed sources, Pereda then decided to overthrow Banzer and seize the presidency - without waiting for the new elections that he himself had requested - after military units throughout the Andean nation agreed to back him.

One informed source here, said the crucial backing for Pereda came after Banzer reneged on a promise to resign from the presidency in favor of a military junta that would have served as a caretaker government until new elections. Banzer's promise reportedly was part of the deal that also called for Pereda to ask that the elections be annulled.

Pereda and much of the military were said to have become suspicious of Banzer's intentions when he failed to live up to his half of the bargain. There was a feeling that Banzer planned to keep control of the government and eventually become a candidate in a future election, if it were held, thus possibly denying Pereda his turn as chief of state, according to the source.

The military apparently decided to stage the coup rather than risk an election flight between Pereda and Banzer that could have resulted in a victory for one of three opposition candidates. Together, they had polled close to a majority of the vote in the election two weeks ago - even with the apparent widespread vote-counting fraud and ballot box-stuffing by Pereda's supporters.

The specter of Herman Siles Zuazo, a dedicated leftist who came in second in the election, winning the presidency in a future election was apparently too much for the military, according to the source, especially if Siles won because Banzer took votes from Pereda.

Whatever the precise reason for the coup, it came as a severe setback for the Carter administration's policy of encouraging human and political rights in Latin America, according to diplomatic assessments here.

Instead of providing an example of a military government turning over power peacefully to a democratically elected government, Bolivia has demonstrated once again that Democracy is a fragile concept in this part of the world, subject to the whims of those in power.

Because the Carter administration become so closely tied to the democratization process, it is felt that the United States must persuade Pereda to hold the second election that he suggested - or demonstrate that a government that aborts an election faces severe international consequences.

At the moment, it appears that Pereda and his military supporters may be willing to risk the consequences. Informed sources said that the new president is now talking about holding another election in two years - not six months - and that he is determined to consolidate his power beforehand.

Pereda swore in a Cabinet yesterday composed of military men and generally right-wing political leaders without great stature in Boliva. The new interior minister, Col. Faustino Rico Toro, is said to be a tough conservative who would not hesitate to use force against real or imagined enemies of the new government.

While La Paz and the rest of the country remained calm, there were reports of arrests of union and human rights leaders in provincial cities, beginnings of what some observers fear will be a wave of repression against those who oppose the military.

Siles, who has gone underground, said in an interview with Reuter Saturday night in the back of a moving jeep. That he will attempt to organize peaceful resistence - principally strikes - to force Pereda to hold elections soon.

Siles, a former president, warned, however, that such peaceful protest "has a limit, which we hope will be understood by the armed forces before it is too late to avoid fratrcidal clashes."