President Reagan is extending economic sanctions against Nicaragua, over the objections of a group of Democratic House members who say he should be helping the peace process rather than punishing Nicaraguans.

The White House announced the move Monday, saying Nicaragua's Sandinista government still poses "an unusual and extraordinary threat to the national security and foreign policy of the United States."If Reagan had not made the formal announcement of a one-year extension with publication in the Federal Register, the sanctions he imposed in 1985 would have lapsed on May 1.

Reagan signed an executive order on May 1, 1985, cutting off all trade with the Central American country, denying Nicaraguan airliners and flag vessels access to the United States and ending a 27-year U.S.-Nicaraguan friendship treaty. Reagan cited "aggressive actions" by Nicaragua and its close military ties with Cuba and the Soviet Union.

The United States, however, has maintained diplomatic relations with Nicaragua, while supporting Contra forces trying to overthrow the government of President Daniel Ortega.

Democratic Reps. Mike Lowry of Washington, Nancy Pelosi of California, Don Bonker of Washington and George Crockett of Michigan had been organizing an effort to lift the embargo, gathering signatures for a letter to the president.

Lowry said Reagan should "stop punishing the Nicaraguan people and start pushing the peace process."

"The Nicaraguan embargo has worked against U.S. interests from the beginning," he said in a statement released by his office. He said it has discouraged the private sector in Nicaragua, brought severe criticism from other Latin American and Western European countries, harmed U.S. business and labor interests "and increased the suffering of innocent civilians in Nicaragua."

Lowry introduced legislation last week to lift the trade and other economic sanctions against Nicaragua.

"If the Nicaraguan emergency were allowed to lapse," Reagan's letter said, "the present Nicaraguan trade controls would also lapse, impairing our government's ability to apply economic pressure on the Sandinista government and reducing the effectiveness of our support for the forces of the democratic opposition in Nicaragua."

Meanwhile in Nicaragua, President Daniel Ortega urged the United States to lift its economic embargo against Nicaragua and warned that he will bar U.S. aid to opposition groups in his country if the trade sanctions continue.

In declarations published Monday in Barricada, the official newspaper of the ruling Sandinistas, Ortega renewed his call for "the government of the United States to stop the war and lift the embargo" against his country.