Nicaraguan military officials said the Sandinista government is suspending, at least temporarily, the draft as part of a freeze on the size of its armed forces and their arsenal.

The use of the draft is believed to have enabled the Sandinista rulers to double the size of the Nicaraguan Army over the last 17 months. Officials say that the draft is suspended for the months of May and June and that it will resume later this year, but only to replace soldiers released from duty or killed in action against the U.S.-backed Nicaraguan rebels, known here as contras or counterrevolutionaries.

The officials said the overall manpower and weapons freeze was the result, in part, of the Sandinistas' ability in recent months to dominate the rebels. But it is also widely known here that the draft has proven unpopular with many Nicaraguans and that supporting the constantly growing Army has drained Nicaragua's already anemic economy.

Journalists who have visited Nicaraguan refugee camps in Honduras and rebel military camps along the Honduran-Nicraguan border recently report an increasing number of young men arriving there and citing the draft as the main reason they left Nicaragua.

In recent months, various Sandinista officials said the contra movement had reached its peak and that it was becoming more difficult for the rebels to find recruits. But it was clear that the draft itself was driving possible rebel recruits across the border into Honduras and into neighboring Costa Rica.

There have been demonstrations, some violent, in several Nicaraguan towns against the draft. Nicaraguan Roman Catholic bishops have condemned the Patriotic Military Service, as the draft is known here, charging that the Sandinistas have used it to indoctrinate young men in Marxist ideology.

In Washington, spokesmen for the Reagan administration and for the rebels fighting the Sandinistas cast doubt Wednesday on reports by a rebel defector that the contras routinely kidnap, kill and rape noncombatants, The Associated Press reported. Bosco Matamoros, spokesman for the Nicaraguan Democratic Force, said the charges by former commander Jose Efren Martinez Mondragon are "outright lies." State Department spokesman Edward Djerejian said the administration had "no information which would substantiate the specific charges."

Sandinista officials have refused to specify the size of the armed forces. Foreign observers have estimated the size of the Army at about 40,000. The number of reserves on active duty is thought to total 20,000 and the militia is believed to include 50,000 persons with access to rifles.

"If you are talking about fighting and defeating the contras, just the contras, then we have all the men we need," said Lt. Guillermo Gonzalez, an Army spokesman. "We have done very well against them in recent months. We have been hurting them. We have been using our Irregular Warfare Battalion and our artillery is really keeping the pressure on them.

"The decision not to expand the size of the Army responds to a military situation, but it is also, I think, an expression of our political will," said Gonzalez. "People accuse us of building an army of expansion to attack our neighbors. That is ridiculous. We have reached the size necessary for our defense and you see we don't need any more men now."

A commission has been formed in the armed forces, said Gonzalez, to decide when the draft call will begin again.

"It is no longer a matter of increasing numbers," said Commander Francisco Rivera, a top official in the political section of the Sandinista Popular Army. He insisted the Sandinistas had met the goals they set when the draft was signed into law on Oct. 6, 1983, and that the Sandinista Front's nine-man National Directorate had made the decision to suspend the draft now.

But a well-placed Sandinista civilian official, who also said the decision to suspend the draft was primarily in response to the favorable Sandinista military situation, added that the draft was causing "social problems" that were a factor in the decision.

Gonzalez tried to minimize the importance of antidraft sentiment, saying that the percentage of draft resisters is small. But he did say that the drafting of young men has had a strong impact on the nation's economy and that freezing the size of the military also answered economic considerations.

"We can't be taking people away from necessary economic paths, away from the coffee and the cotton. We have to stabilize that situation," he said. The Sandinistas say they are spending more than 40 percent of their budget this year on defense.

Gonzalez said that when the draft is resumed, the range of eligibility will be raised to include men between the ages of 17 and 30. The current ceiling is 23 years of age. The draft has seriously depleted the number of young men in the nation's classrooms, and Gonzalez said that the Army was attempting to spread the load.

"And if we don't need more men, then we don't need a greater supply of arms," said Capt. Ricardo Wheelock, special assistant to Defense Minister Humberto Ortega, who confirmed the freeze on Sandinista firepower.

"An Army is always needing to replenish itself, to replace weapons, but it is true that we don't plan to add to our quantity of arms."

A diplomat said, however, "We are 90 percent sure that arms are still coming in, but whether they are additional or replacements I can't tell you."

The Nicaraguan armed forces have received a steady infusion of arms from the Soviet Union and other East Bloc nations over the past five years. The Reagan administration has accused the Sandinistas of staging an unbridled military buildup and of posing a threat to its neighbors. The administration has insisted that the Sandinistas must reduce the size of its armed forces as part of any peace plan.

The Sandinistas, meanwhile, have insisted that the expansion of their armed forces was in response to the rebel attacks and the threat of direct U.S. intervention.

Wheelock said the Sandinistas had reports that the rebels had acquired new shoulder-held antiaircraft missiles and warned that if such a weapon were used by the contras, the freeze on new arms imports would end