UNITED NATIONS, OCT. 8 -- Nicaragua's president, Daniel Ortega, launched a scathing attack on President Reagan today yet renewed his call for a meeting and said it should follow implementation of a Central American peace plan.

Speaking to the U.N. General Assembly, Ortega blamed Reagan personally for 40,000 killed or wounded in the Nicaraguan fighting and criticized the U.S. president's comments on the peace plan in a speech in Washington yesterday.

Later, at a press conference, Ortega cautioned that the recently reopened opposition newspaper La Prensa could be closed again if it "starts to defend the Reagan policy" of funding rebels fighting to overthrow Nicaragua's Sandinista rulers. La Prensa was allowed to resume publication last week in compliance with terms of the peace plan signed Aug. 7 by the five Central American presidents.

He also made clear that his government could not grant amnesties, called for in general terms in the peace plan, to all 2,000 former members of the National Guard and 2,000 rebel fighters convicted of crimes against the state.

Ortega said in his speech that Reagan, by asking Congress to approve $270 million in additional funding for the anti-Sandinista rebels, is "doing something completely out of line" with the peace pact. "It goes dead against the agreement," he said.

Ortega's speech was harsher in its references to Reagan than previous addresses the Nicaraguan president has delivered here. Diplomats suggested that Ortega sees Reagan as more vulnerable now as his term of office nears its end. Diplomats also noted that Ortega probably felt bound to counter Reagan's unexpected praise for the Central American accord in a speech yesterday at the Organization of American States with a hard-hitting analysis of what his government considers the contradictions in the U.S. position.

Ortega said the Reagan statement showed a "flippant and disrespectful attitude" toward all five Central American presidents, who are "leaders of independent sovereign countries, not colonies of the United States."

Ortega said that at the OAS "President Reagan posed as a great judge of the peoples of the world. Who gave him such power?" Later in his speech, Ortega declared, "People do not want Rambos. People want men of peace."

Ortega offered to meet personally with Reagan or other American officials on Dec. 10, five days after an international panel is to make its first report on compliance with the Central American peace agreement, to work out a bilateral arrangement guaranteeing mutual security.

But he again rejected any dialogue with the leaders of the rebels, known as counterrevolutionaries or contras, as the United States has demanded, saying:

"We would gain nothing by talks with the top people in the counterrevolution . . . . The dialogue has to be between the U.S. government and the Nicaraguan government."

Long before Ortega reached that point in his 50-minute speech, the U.S. delegation had walked out of the assembly chamber.

"I refuse to sit there when my country and my president are insulted and lied about," said U.S. Ambassador Vernon Walters in the corridor. He called Ortega's rhetoric "typical revolutionary babble," and said, "We did not impose the totalitarian dictatorship on Nicaragua. He did."

Specifically, Walters rejected a statement by Ortega a moment before the walkout, that "it was a failure of U.S. policy" that led to the Central American agreement. He said the talks were generated by the contras' military pressure.

As Walters was leaving, Ortega interjected that "some people find their ears hurt when the truth is spoken. Some people are incapable of listening." He said the United States had committed aggression and killed Nicaraguans, "but now they are upset when the truth is told them."

Later, Ortega maintained that it was the U..S policy of force that "drove us to set up a state of emergency," but the August peace agreement had made it possible for Nicaragua's Sandinista rulers to ease restrictions on the press and institute a policy of reconciliation with its opponents.