The Sandinista government charged today that U.S.-backed counterrevolutionary forces have made a new thrust across the Honduran border into northeastern Nicaragua and warned that "a broader conflict" with Honduras could result.

The denunciations by Defense Minister Humberto Ortega and Foreign Minister Miguel D'Escoto at a joint news conference were the second time in two weeks that the Nicaraguan leadership has raised the specter of war with Honduras because of recently stepped-up attacks by antigovernment guerrillas directed and supplied from Honduran territory.

They underlined the increasing anger of the revolutionary government here at what its officials describe as a campaign by the Reagan administration, working through Nicaraguan ex-National Guard officers and the Honduran Army, to destabilize the Sandinista leadership that took over Nicaragua in July 1979 after the downfall of the late Anastasio Somoza.

"We do not want to dramatize things, but I think it is obvious that to the degree the Honduran leadership keeps betraying the Honduran people. . .to the degree the Honduran leadership keeps using its territory for harassing the Nicaraguan people, in that degree U.S. imperialism could achieve what it is seeking; that is, a broader conflict, a military conflict," D'Escoto said.

"It is time for Honduras really to choose between recovery of its sovereignty, deciding its own destiny, forging its own relations, or continuing to be used to fight a war that is not a declared war and that has nothing to do with the interests of our peoples." Honduras has denied aiding the rebels.

Ortega said the latest counterrevolutionary attacks came in the steamy reaches of Zelaya province along the Coco River that forms the border between Nicaragua and Honduras. More than 2,000 Miskito Indians, officered and armed by the other counterrevolutionaries, have gathered on the Honduran side of the river, and two units totaling 250 men have entered Nicaragua during the past three days, he said.

Sandinista forces have lost 12 men killed in clashes with the guerrilla units, Ortega reported. One unit crossed near Waspam and infiltrated south toward Santa Clara, he added, while another moved across near the village of Kum, about 15 miles downriver. In addition, he said, the dissident Miskito forces are shooting at Nicaraguan border troops across the river from Honduran territory.

Although the number of antigovernment guerrillas reported in the new Zelaya fighting remained small, Ortega placed the clashes in the context of increased attacks over the past two months in Matagalpa, Nueva Segovia and Chinandega provinces that have taken several dozen victims and raised official concern here to a peak.

"The situation in the last two months represents a very serious situation, because the invasion is getting bigger every day," said Ortega, one of the nine commanders who make up the country's top leadership.

He estimated 800 guerrillas remain in Nicaragua from a force of 1,200 that he said infiltrated from Honduran training camps with U.S.-financed arms in late January and early February to "liberate" a patch of territory from Sandinista control. Most are in mountain redoubts in Nueva Segovia province in the Arenales area, where rugged terrain and lack of roads make pursuit by Sandinista soldiers difficult.

But the clashes in Zelaya are particularly worrisome to the Sandinista leadership for several reasons. First, the undeveloped area, traditional domain of Miskito and other Indian tribes, also has almost no road communications, making government control difficult at best.

In addition, an estimated 13,000 of the Miskito Indians have fled into Honduras. They have gone to refugee camps near Mocoron, becoming a ready manpower pool for counterrevolutionary organizers.

Exiled leaders in Miami and Costa Rica say one Miskito leader, Brooklyn Rivera, has allied his followers with anti-Sandinista figures such as Eden Pastora and Alfonso Robelo headquartered in San Jose. Although there are occasional reports of clashes near the Nicaraguan-Costa Rican border, this group is said to be short of funds and capable of little military action.

Another Miskito leader, Steadman Fagoth, has forged a rough alliance with the main counterrevolutionary group, the Nicaraguan Democratic Force. Reports from the exile groups say he has benefited from funds and training that according to U.S. press reports and Nicaraguan officials have been arranged by the U.S. CIA with the help of Argentine advisers and Honduran Army officers. It apparently was to these forces that Ortega was referring today.

Aside from perennial resistance to Managua's authority, the Miskito Indians also have become willing candidates for antigovernment action because of resentment at the forced relocation of about 12,000 Miskitos early last year inland from traditional areas along the Coco River to government-financed centers.

It was to escape the relocation and pressures from the Sandinista government that the other Miskitos fled into Honduras, reliable sources in the area have reported.