After three years of media censorship, the Nicaraguan government has begun talks with executives of the only opposition newspaper about the possibility of ending the limits on press freedom.

But most observers consulted here say that the Sandinista government, challenged by armed rebels and the hostility of the Reagan administration, would find it almost impossible to lift censorship.

Vice President Sergio Ramirez met March 7 with two executives of the opposition newspaper La Prensa. According to one of the executives, the Sandinista leader asked them how their newspaper would treat his government if censorship were lifted.

"He asked what the political line of the newspaper would be," Jaime Chamorro said. "We told him our line has not changed. We are not afraid of social change or of changes in government structure, but only within western democratic norms. We are against alignment with Cuba, the Soviet Union and the Eastern Bloc."

The Sandinistas, according to diplomats and government officials, are under pressure from key European and Latin American governments, as well as the Reagan administration, to end censorship.

Some Sandinista officials have told journalists that they favor ending press control, which they say has turned La Prensa into a cause celebre and damaged the Sandinista image internationally. Others have insisted that the afternoon daily must be controlled, charging that it is an instrument of the Reagan administration and the CIA and is allied to the rebels trying to overthrow the government.

Diplomats and other nongovernment observers said that given the deepening economic problems, difficulties with draft resistance and the rebel conflict, it was unlikely that the Sandinistas would end censorship now. Vice President Ramirez confirmed that the meeting had taken place but refused further comment.

Chamorro said the vice president has asked the executives of the newspaper to draw up a position paper, in effect a list of issues La Prensa would insist on covering if censorship were lifted.

"We will never agree to self-censorship," Chamorro said. "True freedom of the press comes without conditions."

A major Sandinista concern is how La Prensa would deal with news about military operations against the rebels. Chamorro said the newspaper's executives and editor are drafting answers to Ramirez on that and other issues.

Ramirez "said the Sandinistas realize La Prensa is an institution in Nicaragua and will survive," said Chamorro, whose family founded the newspaper in 1926. "He said we must realize that the Sandinista Front is an institution that will also survive and that we must learn to live together."

Chamorro's brother, Pedro Joaquin, who was editor of La Prensa, was a strong critic of dictator Anastasio Somoza, and was assassinated in 1978, reportedly by Somoza's allies. The slaying intensified opposition to Somoza that eventually led to his ouster by the Sandinistas and others in July 1979.

Censorship of all Nicaraguan media began March 15, 1982, as part of a state of emergency declared after U.S.-backed rebels blew up two bridges near the Nicaraguan-Honduran border. The government also closed 22 independent radio news shows, which have remained off the air ever since. Both television channels here are controlled by the government.

Chamorro said censorship diminished during the three-month national electoral campaign last summer and fall, but on Nov. 8, four days after Sandinista candidate Daniel Ortega was elected president, the government imposed new, stricter censorship.

"They diminished censorship during the campaign to try to convince foreign governments they were being democratic," said Chamorro. "Then they gave foreign election observers four days to get out of town, and they came down hard on us."

According to the guideliness of Nov. 8, Chamorro said, the media were not allowed to raise doubts about the validity of the elections, could not report on strikes or other labor disputes, were prohibited from publishing any account of a military operation that did not come directly from the government and could not report any criticism of the government or the Sandinista Front from outside Nicaragua.

According to Chamorro, almost half of the material on the newspaper's three main news pages was censored during December, January and February. He said censorship was lighter in March.

In November, after the elections, the then-editor of La Prensa, Pedro Joaquin Chamorro -- son of the slain editor -- left the country. In December he announced that he would stay in voluntary exile until full press freedom is granted. He recently signed a document in Costa Rica, along with other civilian and military opposition leaders, calling for the Sandinistas to negotiate peace with the rebels and to hold new elections.

Jaime Chamorro, his uncle, was summoned to appear before the chief of state security, Lenin Cerna, after allegedly telling a group of visiting Americans that the United States should continue to support anti-Sandinista rebels, whom he considered "fundamental to prevent . . . the implantation of a communist state."

Chamorro did not deny making the statement.

"It was a friendly meeting," said Chamorro. "He told me to watch my step because he didn't want to have people following me all the time watching everything I do."