President Reagan's hard line against the leftist Sandinista government of Nicaragua is "not helpful" to the country's democratic critics, opposition leader Arturo Cruz said yesterday.

He added that the recent election of Daniel Ortega as president of Nicaragua may lead to progress towards a regional peace and said the Reagan administration "should give Ortega a period of grace" in that hope.

Cruz, a former member of the Sandinista government, said at a news conference that the invasion alert called by Nicaragua in response to U.S. troop movements and threats has included tighter censorship, restrictions on public meetings and a crackdown on dissidents.

"The situation diminishes the stamina of the democratic opposition within Nicaragua," said Cruz, who now heads the Democratic Coordinate opposition coalition.

Cruz said it made him "very, very sad" to know that U.S. airplanes have been flying at supersonic speeds over Nicaragua so that their sonic booms alarm the population. "I become very, very distraught when I see foreign vessels surrounding my country," he said. Later, he noted that his speaking tour of the United States "is taking place at the most difficult time for me."

Cruz said he did not think the Sandinistas "will take the first step in generalizing war in the region," but he added, "they are ready if another country takes that step."

The Reagan administration has defended its policy of constant pressure on Nicaragua as successful in building domestic resentment against the Sandinistas. Current military exercises near there coincided with administration leaks that Nicaraguans might be about to receive Soviet Migs. That concern has since abated.

Ortega became president of Nicaragua in Nov. 4 elections that "crowned the king," Cruz said. "Ortega will be something more than primus inter pares first among equals , and he has to be" in order to hold out against factions in the government who think regional war is inevitable, Cruz said.

Ortega's faction in the nine-member Sandinista leadership is the most moderate, and "Ortega will make an effort to reach national conciliation," Cruz said. "But I have doubts that his efforts will be sufficient."

Ortega's vote was 67 percent of the total, but less than 50 percent of Nicaragua's registered voters, Cruz said. He noted that 20 percent of the vote went to opponents and that many ballots were deliberately spoiled in protest. "It is a sobering lesson for them," he said.

Cruz acknowledged that U.S.-backed rebels fighting the Sandinistas were drawing more recruits as the Nicaraguan economy crumbles, but said eliminating U.S. support for the rebels was still "desirable." He added, however, that it "should be part of an overall political solution."

Cruz spoke at a news conference with former U.S. ambassador to El Salvador Angier Biddle Duke and William C. Doherty, head of the American Institute for Free Labor Development, announcing formation of a private educational organization called Prodemca, to promote democratic forces in Central America.

Duke said the nonprofit groups's 35-member national council would cut across traditional party and ideological lines in order to "search for the moral high ground" in Central America. Its members include former agriculture secretary Orville L. Freeman, business executive J. Peter Grace, American Federation of Teachers President Albert Shanker, Boston University professor Elie Wiesel and New York attorney Morris B. Abram.