Last August the Nicaraguan rebels known as contras had just staged two successful ambushes, were awash in supplies, and said that their war against the Sandinista government was going their way.

"Come back in six weeks, and we'll have more victories to tell you about," said Frank Arana, spokesman for the Nicaraguan Democratic Force, the largest contra group.

Today, six months later, the contras -- or counterrevolutionaries -- have little reason to boast. Between 60 and 70 percent of their forces have been staying in base camps in southern Honduras since October, and it is unclear when they will cross back into Nicaragua to continue their war, according to contra sources and other informants.

The rebels' lack of military activity has led to dissatisfaction among many of their U.S. supporters, including some U.S. officials close to the program and some members of Congress who have backed it in the past. Questions have been raised about the contras' ability to wage a guerrilla war, about their willingness to fight, and about the U.S. government's management of $27 million of nonlethal aid for the rebels.

A well-placed source said that there was "concern" within the U.S. government about the performance of the contras. "The problem is, if the contras won't fight, then what are the alternatives" for dealing with the Sandinistas, the source asked.

From the U.S. government perspective, the contras' poor showing suggests, at best, that they are far from reaching their goal of overthrowing the Sandinistas. At worst, it indicates that they will remain only an irritant to the left-wing government in Managua.

The contras sent up to 10,000 combatants, the bulk of their forces, into Nicaragua in June and July in an effort to stage their first sustained offensive of the year. But a Sandinista counteroffensive in early autumn, backed by increased use of Soviet-made helicopter gunships, cleared most contras out of their old strongholds in the coffee-rich mountains of northern Nicaragua, rebel leaders said.

As a result, the guerrillas have been less successful than a year ago in disrupting the vital coffee harvest, which is coming to an end now, they said.

The contras' only substantial presence currently is in cattle-producing regions in the south-central part of the country, according to the contra officials. Even there, however, they have had only one significant victory since August, an attack that reportedly killed 33 Army reservists at the town of Presillitas on Nov. 10.

The contras have been unable to build an effective clandestine network of supporters inside Nicaragua to deliver supplies to guerrillas in the field, according to contra leaders and other sources. As a result, they must rely on a few aircraft for parachute drops to their forces, the sources said.

One reason for the contras' troubles is the Sandinistas' improved military performance. The Sandinista Popular Army, reportedly aided by Cuban advisers, appears to have had much success in cutting off the contras' infiltration routes in northern Nicaragua, according to diplomatic and military sources.

But critics charge that the rebels' leadership lacks a clear strategy for waging a guerrilla war, and that the contras' forces are relatively unaggressive. They note that El Salvador's left-wing guerrillas, with less than half as many combatants and without a sanctuary in a neighboring country, have had much greater military success.

"There isn't the kind of ideological commitment within the contras that you find with Marxist guerrillas," a source familiar with the contras' activities said. The contras apparently prefer to wait in Honduras, where they can buy food easily and send the bills to the U.S. government, rather than return to Nicaragua, where it sometimes is hard to get food, the source said.

Rep. Dave McCurdy (D-Okla.), who played a key role in putting together the congressional majority that approved U.S. aid for the contras last year, said in an interview, "A number of us are disappointed in both the military and political progress of the contras."

He said that the contras did not espouse a clear political program, other than opposition to the Sandinistas, and that their large "task force" units of several hundred combatants were inappropriate for a guerrilla war.

"I don't sense, as they're structured and organized, that they can be a military threat. What you need are highly disciplined, tightly unified units that have different tactics than they have had in the past," McCurdy said. Contra leaders say their forces have begun traveling in smaller units to deny easy targets to the Sandinistas' helicopters.

Both the contras' leaders and U.S. officials said the rebels' main problem is a lack of supplies, and particularly of high-quality combat boots. As a result, they said, it is critical that Congress approve fresh aid for the contras as the Reagan administration has proposed.

"At the end of September, and in October, we began to feel the impact of a lack of supplies," said Indalecio Rodriguez, a member of the Nicaraguan Democratic Force's seven-member directorate. Other contra leaders, including military commander Enrique Bermudez, said that the rebels were able to operate at only 50 percent of their capacity in 1985 because of the shortage of gear. But Bermudez had said in an interview in late August that "we have the supplies to continue fighting at this level."

Both contra officials and other sources said that the rebels have adequate supplies of rifles, ammunition and other military equipment. The serious shortage, they said, was of boots capable of holding up during treks of many weeks into Nicaragua from Honduras.

When asked why they cannot buy boots in Honduras, and send the bills to the U.S. government, contra leaders said that the only boots available locally fall apart in several weeks. El Salvador's guerrillas wear those same boots, smuggled in from Honduras. But contra leaders noted that El Salvador is a much smaller country than Nicaragua.

The $27 million of U.S. nonlethal aid was designed specifically to meet the contras' requirements for such supplies. Hundreds, or even thousands, of pairs of U.S.-made combat boots are said to be stored in New Orleans waiting to be sent to the contras. But many of the deliveries have been blocked because of a four-month-old dispute with the Honduran government, and several well-placed sources said that the United States still has not been able to resolve it.

Honduras' former president, Roberto Suazo Cordova, blocked flights into Honduras to deliver the gear after a U.S. television crew flew in aboard the second such flight on Oct. 10. Honduras officially does not admit that the contras are based on its soil, and the publicity about the flight embarrassed the government.

In addition, Suazo Cordova was seeking to pressure the United States to disburse $50 million of promised aid, and to stop acting to block his own efforts to remain in office beyond his term. According to one reliable account, several Honduran military officers offered to allow the deliveries behind Suazo Cordova's back, but the State Department objected on grounds that such a move would undermine civilian authority in Honduras.

Honduras' new president, Jose Azcona, was widely expected to lift the ban on aid flights for the contras after he took office on Jan. 27. So far he has not done so, according to several sources, who said that a recent armed forces leadership shake-up had delayed his decision.