ALONG THE HONDURAS-NICARAGUA BORDER, DEC. 22 -- The commander of anti-Sandinista forces claimed today that a two-day offensive against three remote mining towns in northeastern Nicaragua was the largest and most successful ever and showed that the rebel forces can carry out attacks against important targets throughout the country.

The rebels, he said, had no intention of holding on to the territory attacked since that would subject his forces to possibly costly retaliatory ground and air strikes from much larger government forces.

Enrique Bermudez, the commander of the northern front of the the Nicaraguan Resistance, said here today that the 4,400 troops used in Sunday's attacks were withdrawing today from the town of Bonanza and that rebel troops left Siuna yesterday and had disengaged from fighting around La Rosita, the only community not completely overrun. They were to return to their normal operating areas, he said.

"We hit them hard," he said. "We achieved all our objectives."

Although the attack appeared to be the most ambitious undertaking by the U.S.-backed rebels known as contras in their six-year war against the leftist government, the area under siege, about 150 miles northeast of Managua, is largely inaccessible and there has been no independent confirmation of claims by either side.

In Managua, the government said its Popular Sandinista Army was in control of all three towns and that the contras "are fleeing to their sanctuaries with the Sandinista Army on their heels." The official news agency said at least 150 people -- 70 contra fighters, 30 government troops and 50 civilians had been killed, Reuters reported. Bermudez said his initial reports said there were more than 100 Sandinista dead.

Bermudez said the primary goals of the operation were the destruction of important radar installations used to monitor supply flights to the rebels, and ammunition depots in Siuna, a town of 12,000, as well as the destruction of a hydroelectric generating plant in Bonanza used to run the mines. All were accomplished, he said.

Aside from the military objectives, Bermudez said the rebels wanted to disrupt the gold and silver mining operations that earn needed foreign exchange for the Sandinista government.

{In Washington, State Department officials said the attack signified the evolution of the contras from a rather rag-tag fighting force to one that is capable of carrying out much more sophisticated assaults and of massing more than 4,000 troops, with support from local populations, for surprise attacks.}

Bermudez spoke to a small group of reporters at a rear base hidden in the dense jungle not far from the Coco River which forms the border between Honduras and Nicaragua. The reporters were taken there on the condition they not reveal its exact location or how they got there.

The reporters had been told they would visit one of the captured communities, but the trip was canceled by the contra command this morning because it was considered too dangerous.

Bermudez said the jungle base where he spoke was not the command and control center from where the battle was directed.

While acknowledging the attacks, the Sandinistas initially said only about 1,000 rebels took part. Today, however, Sandinista officers in Mangua raised the total to 3,000.

Bermudez emphasized the planning that went into "Operation Commandante Olivero," named after a fallen rebel, and he showed reporters an extensive battle plan.

The attack was conceived two months ago, and it was originally scheduled for the end of November, Bermudez said. He added that it was not possible to get all the troops into position by that time. Thus, he claimed it was a coincidence that it was launched the day before rebel negotiators were to meet Sandinista representatives for a second round of cease-fire talks in the Dominican Republic.

The peace talks were called off after the rebel delegation refused to meet an American lawyer and a West German politician representing the Sandinistas.

The talks were part of the effort by area governments to negotiate an end to the region's wars. The presidents of Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica are scheduled to meet next month to judge the success of the pact, signed in August.

The collapse of the cease-fire talks raised the possibility of further heavy fighting over the holidays.

The two sides had earlier agreed on a two-day truce for Christmas Eve and Christmas Day but it was not immediately clear, in the light of the recent fighting, whether they would abide by the cease-fire.

Bermudez made it clear he did not think the peace plan would work.

"The peace plan has already failed. Nov. 5 was the date. The Sandinistas hope they can keep harassing us with the plan for six or eight months more" until the rebels disappear, he said.

Contradicting initial reports, Bermudez said the attacks on the three mining communites were carried out with 4,400 men. Another 2,600 were used in diversionary attacks along the Rama Road, to the south, bringing the total for the operation to about 7,000, the number initially used by contra spokesmen announcing the attack.

Following the attack Sunday, Bermudez said his troops controlled Siuna and Bonanza for more than a day. They did not capture La Rosita, although rebel troops destroyed the installations at the airstrip there, Bermudez said.

Besides destroying military targets in the three towns, Bermudez said the contras captured large quantities of military supplies and food.

The Sandinistas did not deploy their attack helicopters because of fears of rebel antiaircraft missiles, Bermudez said. Planes flying between 8,000 and 10,000 feet, higher than the range of the missles, were used to bomb the towns, he said. The bombs, dropped from Soviet-made AN26 transports, missed their targets, he said.

"This region has all the characteristics for an attack. It's isolated. Where can reinforcements come from?," he said.

As an example of how well coordinated the attack was, Bermudez said rebel forces were set in ambush along the two roads leading into Siuna and their actions against convoys of reinforcements delayed the arrival of those reinforcements for about 24 hours.

"We are aggravating the {economic} crisis and we are showing our ability to hit them where we are. The cost to us was minimal . . . and we are in a position to continue hitting them," he said. Bermudez added that more attacks were being planned.

He said some troops walked more than two weeks without being detected to position themselves for the attack, Bermudez said.

Washington Post staff writer Joe Pichirallo contributed to this report.