Nicaragua's revolutionary leaders marked the beginning of their third year in power today with announcements of wide-ranging nationalizations and a careful downplaying of their massive buildup of military forces.

Speaking from a platform festooned with flowers to more than 250,000 people, junta member Daniel Ortega outlined agrarian reforms dewsigned to take unproductive farms away from their private owners and turn them over to cooperatives and other groups that might make them work.

Ortega also announced new legal procedures for prosecuting industrialists found to be smuggling capital out of the country and decreed the immediate nationalization of 13 companies whose owners were believed to be involved in such activities.

Distribution of sugar and other export commodities worth about $40 million a year also will be nationalized, Ortega said.

Ortega and Interior Minister Tomas Borge, the only other major speaker at today's rally, emphasized a commitment to a mixed economy and conceded that some private business men have worked for the benefit of the country. But Ortega said the nationalizations nevertheless are necessary to "put our house in order."

Ortega criticized many businessmen as virtual "traitors." But he also noted the "sabotage of undisciplined workers."

From now on, Ortega said, takeovers of land by groups of peasants will not be permitted. He said the new law makes them unnecessary. But it was also clear that the Sandinista leadership is eager to do away with the unpredictable land occupations that have helped destroy any atmosphere of confidence among Nicaragua's major farmers.

There was the usual anti-imperialist language common in Nicaragua and several accusations against the United States for past injustices, including the cutoff of what Ortega calculated to be $81.1 million in aid and the presence of counterrevolutionary groups training in Florida.

Nevertheless, the hostility toward Washington was not nearly so strident as on past occasions. Ortega seemed intent on leaving the way open for renewed and improved relations.

"Before the United States we are flexible," said Ortega, even if the Sandinistas must remain firm on certain points.

Yet despite the crowd that filled the July 19 Plaza and the decrees that, when more clearly articulated, could change basic aspects of the country's economy, this year's celebration was most conspicuous for what it lacked.

Gone was the fierce enthusiasm, the exaltation of triumph of July 19, 1979, when 50 years of the Somoza dictatorship came to an end, and the ragged guerrillas, the poor from the sprawling slums and the businessmen from their offices poured into the streets to celebrate.

Gone were the host of foreign leaders -- Cuba's Fidel Castro, Grenada's Maurice Bishop, former Venezuelan president Carlos Andres Perez and a high-level delegation from the United States -- who attended the first anniversary celebration. No foreign leader came to Managua for this year's festivities.

Where the parade ground was filled in 1980 with East German military trucks, rank upon rank of soldiers and militia, captured tanks and the roar of military airplanes overhead, this year there was only a line of militiamen controlling the crowds.

Although Borge said flatly that "where we get out arms is our business," the Sandinistas are clearly aware that the announced buildup of their armed forces has helped provoke rising tensions throughout the region. The celebration today seemed designed to keep those tensions from being made worse with gratuitous shows of strength.

Such a move is typical of this revolution that finds itself, in Ortega's words, facing a world that is "difficult and complex."

The Sandinista leadership has found itself almost overwhelmed by the transition from guerrillas to administrators. Some, frustrated by the constraints of their new role, hunger to follow in the footsteps of guerrilla leader Eden Pastora -- the famed "Commandante Zero" -- into other countries to find other wars in which to fight.

But among those who stay, it appears that the more moderate and pragmatic elements are winning out. Whilte the reforms announced today are extensive, they are not nearly as wide-ranging as those promoted by Washington in nearby El Salvador.

As one Sandinista official said privately earlier this week, "The way we see it, the agrarian reform is farther ahead in a fascist country like El Salvador than it is here.At least on paper. We had to do something."

While constant pressure is exerted against basic freedoms, those freedoms still exist.

The newspaper La Prensa, despite constant verbal and occasional physical mob attacks, continues to publish. Even with the reforms, more than 50 percent of the economy is likely to remain in private hands, and while the level of militarization and police presence has grown considerably in the last 18 months, even U.S. Ambassador Lawrence Pezzullo maintained recently that "there is no such thing as a halfway police state. . . . If you would characterize this as a police state, it is a sort of class-B movie version of a police state."