Nicaraguan President Daniel Ortega, defending last week's imposition of sweeping restrictions on civil rights, said today that they were necessary to prevent "terrorism, sabotage and assassination attempts" by opponents of the Sandinista government.

Ortega, in New York for the 40th anniversary session of the United Nations, said in an interview that the government also had to crack down on the press and on activism by Roman Catholic priests to prevent "propaganda" against the draft at a time when many Nicaraguan soldiers are winding up their two-year hitches and new recruits are preparing to enlist.

Outside his plush suite at the United Nations Plaza Hotel, security was tight. But Ortega appeared relaxed, joking about a morning jog in Central Park. He is to address the General Assembly Monday.

To repair what he acknowledged was a "public relations" problem in the wake of the new restrictions on civil liberties, Ortega has planned meetings with dozens of heads of state and other foreign officials as well as a television appearance on "The Phil Donahue Show."

The extension of a state of emergency nationwide, announced last Tuesday, reinstated and broadened restrictions that had been eased during last summer's election campaign. Although it was unclear how strongly the new limits would be enforced, press censorship was reaffirmed and legal rights of freedom of speech, assembly and travel, as well as the right to form labor unions and to strike, were suspended.

The Reagan administration sharply criticized the crackdown as "a further step toward imposing a totalitarian regime on the people of Nicaragua." Supporters of the Sandinistas here and in Europe were also critical.

Today, Ortega sought to play down the severity and scope of the measures. "We are not liquidating active labor unions," he said. "Political parties can continue to have meetings, so long as they request permission from the authorities. . . . There is not a state of siege. People can walk around where they want to and at whatever hour they want."

The new restrictions would continue, he said, until the Reagan administration reverses its goal of "trying to overthrow the Nicaraguan government."

Ortega said, "We decided to impose this state of emergency because the CIA, which is directing the mercenary forces, is now preparing a counteroffensive, relying more on the Honduran Army, and at the same time trying to attack on an internal front with terrorist activities."

He predicted that the contras, as Nicaragua refers to the rebel forces, would be held back at the border and would be unable to advance without more help from the Honduran Army or direct involvement of U.S. troops.

"We are on the verge of a strategic victory," Ortega said. "It's a question of months . . . we're not concerned about whether the contras get more or less aid. Whether they get a million guns or a hundred million dollars from the Reagan administration, we couldn't care less . . . no matter how much aid they get, it will not change things."

The government prevented the publication of a new newspaper by the Catholic Church and occupied diocesan offices recently, he said, because priests have encouraged draft dodgers who claim to be seminarians.

*The Nicaraguan Catholic Church's Episcopal Bishop's Conference released a statement in Esteli charging the state of emergency curtails "indispensable and fundamental rights," United Press International reported. Cardinal Miguel Obando y Bravo said mass for 5,000, a gathering that was considered a test of the new restrictions.

Ortega compared the emergency decree to the U.S. incarceration of Japanese Americans during World War II. "We are talking about exceptional measures, wartime measures," he said.

Ortega said that the economy had been critically injured by the U.S. trade embargo but that new avenues of commerce were opening up. New sources of agricultural and industrial technology were being explored in Western and Eastern Europe to replace U.S. parts and equipment, he said.