President Anastasio Somoza said today that rejection a U.S. sponsored peace plan by both his government and Nicaragua's political opposition meant that "each side will have to make some kind of concessions" if renewed violence is to be avoided.

He said, however, that his resignation is not among the concessions he is prepared to make. The opposition demand that he and his family leave the country, Somoza said, is both unconstitutional and would mean "taking away my human rights."

The U.S.-backed plan, which called for a nation-wide referendum on his continuing presidency, provided for Somoza's resignation and departure from the country if he lost. The opposition rejected the proposal because, it said, a fair vote is impossible under the repressive Somoza government.

Sources close to U.S. officials who are attempting to mediate between Somoza and the Broad Opposition Front coalition said that their joint rejection of the plan meant the mediators will "have to tkae some new initiative." The sources denied that the seven-week-old mediation effort had failed.

The United States, Guatemala and the Dominican Republic serve on the international mediating team that has unsuccessfully sought to bring Somoza and the opposition to an agreement that would avoid a resumption of September's civil war.

Asked whether he thought the United States still supports his government, Somoza said only that he did not think "the United States is trying to overthrow me."

Although Nicaragua is tensed for the imminent outbreak of violence, and sporadic gunfire and bombs exploded in several parts of the capital Friday night and early today, an anticipated attack by Sandinista Liberation Front guerrillas who led the September battles has not come.

Somoza also denounced the OAS Human Rights Commission, which last week issued a report charging his government's National Guard troops with numerous atrocities during and after the September fighting.

He said he flet "defrauded" and "disillustioned" with the commission.

Somoza accused the commission of using a "double standard" by publishing its reports, without including the government rebuttal it had received and - contrary to its usual slow procedures - barely five weeks after conducting an on-site investigation here.