MANAGUA, Nicaragua (AP) _ Violeta Chamorro, whose opposition newspaper La Prensa resumes publication this week - uncensored, the government promises - says she will keep up the fight that cost her husband his life and divided her family.

''We want liberty,'' Mrs. Chamorro said in an interview last week at La Prensa's offices. ''We left one dictatorship and entered another.''

In compliance with the new regional peace initiative, Nicaragua's leftist Sandinista government agreed last week to allow La Prensa's presses to roll again and the Roman Catholic Church's radio station to go back on the air.

La Prensa was shut down in June 1986 after the U.S. Congress approved $100 million in aid for the Contra rebels. Radio Catolica was closed 18 months earlier for failing to broadcast President Daniel Ortega's year-end speech.

Both plan to be operating again by Thursday.

There was a sense of jubilation around La Prensa last Friday. Carpenters joked while pounding nails into office dividers. Three youths sang while hauling equipment and as a secretary filled out employment forms.

Rolls of newsprint marked ''Made in the USSR'' sat on the floor in a nearby building next to dusty presses and old copies of the paper bearing the slogan ''In the Service of Truth and Justice.''

''Actually, it's very bad newsprint,'' said Mrs. Chamorro, 57. ''We don't like Russian paper, but newsprint is hard to get. So we'll hope for other donations.''

The paper hired 120 people for the reopening. When the paper closed it had 230 employees.

Mrs. Chamorro, president of La Prensa's board of directors, said the paper would follow its longstanding tradition and ''continue fighting for freedom of the press, amnesty, rights.''

Those goals exacted a heavy toll on her prominent family. Pedro Joaquin Chamorro, her husband and the paper's former publisher, was killed on his way to the newspaper in January 1978 by gunmen working for right-wing President Anastasio Somoza.

The assassination helped galvanize support for the Sandinista-led popular revolution, which won out 19 months later.

Mrs. Chamorro became known as ''First Lady of the Revolution,'' serving on the first Sandinista junta for nine months after Somoza's overthrow.

''I wasn't prepared for such responsibilities,'' she said. ''This government didn't meet its promises. They are Marxists.''

Mrs. Chamorro applies the same label to two of her four children. Daughter Claudia is the Sandinista ambassador to Costa Rica. Son Carlos Fernando directs the official party newspaper, Barricada.

Another son, Pedro Joaquin, lives in exile and serves on the directorate of the Contra's Nicaraguan Resistance. Daughter Cristiana works with her mother.

''Many families are divided,'' Mrs. Chamorro said.

In allowing La Prensa to reopen, the government promised Mrs. Chamorro that the paper could publish without censorship.

As Mrs. Chamorro tells it, Ortega, accompanied by Costa Rican Foreign Minister Rodrigo Madrigal Nieto, worked out the reopening in a meeting at her home on Sept. 19.

''I said to Rodrigo that the paper had to be completely free,'' she said. ''Mr. Ortega came to the house and said we could, and he would help.''

The regional peace initiative, signed by Ortega and the presidents of El Salvador, Costa Rica, Guatemala and Honduras last month, calls for freedom of speech and other democratic reforms by Nov. 7. It also aims to achieve cease- fires in Nicaragua and El Salvador, amnesties and an end to foreign backing of rebel groups.

Nicaragua pledged to comply in hopes of ending the five-year insurgency of the American-trained and supplied Contras.

Mrs. Chamorro said she holds out hope that the plan will bring peace and an end to what she says is ''Marxism that the people don't want.''

And if the government tries to censor La Prensa again?

''I'll close immediately,'' she said.