More than 1,000 Nicaraguan troops have crossed into Honduras to battle anti-Sandinista guerrillas, known as contras, in the largest incursion into Honduran territory in the four-year-old conflict between Nicaragua and the rebels, according to diplomatic sources in the Honduran capital of Tegucigalpa.

The sources said that two battalions of Nicaraguan troops, estimated to number 1,400, moved into El Paraiso province in Honduras Saturday and have penetrated about nine to 12 miles. Heavy fighting was said to be under way in the vicinity of the main contra base camps inside Honduras and near the Nicaraguan border.

The sources said that the Nicaraguan Army, apparently anticipating attacks by the contras linked to U.S. congressional votes on aid for the Nicaraguan rebels, had moved their troops close to the border and then pushed across.

The Nicaraguans reportedly entered a triangular slice of Honduran territory, in eastern El Paraiso province, that juts into Nicaragua. The contras are known to have their main base camp and their principal training installation there.

Thus far, the sources said, there has been no contact between the Sandinista forces and the Honduran Army.

The Honduran government has said nothing officially about the action. The chief armed forces spokesman said in a telephone interview today that "up until now we have nothing official on this. I can't confirm anything."

The Honduran government's silence about the reported incursion created an embarrassing problem for the U.S. administration, which was eager to publicize the information.

A senior U.S. official in Washington, speaking to reporters this morning on a not-for-attribution basis, was the first to spread word of the Nicaraguan action. He said that the reports were unconfirmed, but apparently was cautious only because he did not want to contradict the Hondurans.

The reported incursion could embarrass the new government of Honduran President Jose Azcona. An announcement concerning the incursion would confirm the presence of Sandinista troops on Honduran soil and also the presence of contra bases, which is not officially acknowledged.

There have been border clashes between the Sandinista and U.S.-backed rebel forces as well as frequent incursions by the Sandinistas. Most have been small scale, but last May a battalion-sized Nicaraguan unit crossed the border.

The current incursion, diplomatic sources said, appears to be the biggest and may also be the deepest.

Earlier today, in Washington, a senior administration official said the United States had received preliminary reports of a major Nicaraguan incursion involving "well over 1,000 Nicaraguan troops."

Briefing reporters at the White House, the official, speaking on the condition that he not be identified, said that the unconfirmed reports indicated that the operation was larger than previous penetrations.

U.S. officials later reported that the Sandinista forces had penetrated 16 miles into Honduras, prompting private appeals from the government in Tegucigalpa for U.S. "logistical help."

A senior administration official called the action "the deepest penetration" by Nicaraguan troops into Honduras and said "we're very concerned about it."

At a luncheon meeting in Washington, Nicaraguan Ambassador Carlos Tunnermann said he did not believe the White House reports. He said, "The official position of the White House and the Honduran government is that there are no contra bases in Honduras. So who and what is being attacked?" he asked.

The last cross-border attack came the day before last Thursday's House vote against contra aid and "was a contra attack inside Nicaragua, which our Army effectively repelled," Tunnermann said.

In Nicaragua, where government offices were shut and much of the country was on a pre-Easter break, official reaction was limited.

A Defense Ministry spokeswoman, Capt. Rosa Pasos, said, "We are not saying anything. These are just rumors."

Fighting between forces of the ruling Sandinista National Liberation Front and the contras has picked up in recent weeks in the Nicaraguan provinces of Esteli, Nueva Segovia and Madriz, as the Sandinistas responded to contra attempts to reinfiltrate from Honduras by mobilizing more troops into those northern areas.