SAN SALVADOR, OCT. 25 -- With peace talks stalemated and the rainy season ending, the government is bracing for a new round of attacks by leftist guerrillas, who paralyzed the country less than a year ago with their biggest offensive in El Salvador's 11-year-old civil war.

A senior rebel source in the capital said that a thunderous mortar barrage launched at the air force headquarters last week was to have been the start of a series of large-scale assaults at military installations.

The plan was put on hold, he said, after the U.S. Senate voted last Friday to cut U.S. aid to the Salvadoran armed forces to $42.5 million -- half the amount sought by the Bush Administration. He said the congressional move caught the guerrillas by surprise and generated an internal debate about what to do next.

In war-torn areas around the country, government soldiers and guerrillas of the Farabundo Marti National Liberation Front (FMLN) say they are ready to fight.

For example, in Las Vueltas, a rebel-controlled village in the north near the Honduran border, guerrilla fighters gathered in the main square said they were prepared to press their war against the government. "We're ready for a new offensive at any moment," said one rebel, with the cocky calm of a teenage warrior.

About 15 miles to the west, in a barren valley known as El Paraiso, workmen have put the finishing touches on a 10-foot-high cinderblock wall around the army's sprawling 4th Brigade headquarters. Inside the fortified base, a grim-faced officer said, "We expect a new offensive, and we're prepared for it."

Last year, a fall offensive by the FMLN left more than 2,000 dead in the fiercest fighting in the nation's civil war. The offensive, launched Nov. 11 in the capital and other cities, startled Salvadoran officers and their U.S. military advisers, who had suggested the rebels strength was in eclipse.

After the armed forces counterattacked, using helicopter gunships, air-launched rockets and, on several occasions, aerial bombing, the insurgents were driven out of the capital. But the fighting dragged on for nearly a month and gave a new cast to a conflict the government believed it was winning.

Rumors of a new offensive have persisted since the beginning of this year and have intensified in recent weeks. The mortar attack on the air force headquarters Oct. 17 was the third on a military installation in the capital this fall. Then, in a botched attack Tuesday night, a rebel mortar apparently aimed at the Defense Ministry fell short of its target, killing two youngsters at a private home in a residential neighborhood.

While Salvadoran military commanders -- who have put their troops on the highest state of alert twice in recent months -- have declared that such attacks signal the start of a major new offensive, so far they appear to be not much more than noisy feints.

It appears that neither harassing attacks nor a major offensive is likely to change the military balance in the war, which seems fixed in stalemate despite shifts in both sides' tactics and $1 billion in U.S. military aid to the government in the last decade. Rather, the FMLN's threat to unleash a new offensive seems designed to jar loose concessions from the government in peace negotiations sponsored by the United Nations. Five rounds of talks so far this year have produced little progress, and each side has accused the other of inflexibility.

There is little doubt that the rebels are capable of mounting a formidable military offensive. FMLN commanders, diplomats and Salvadoran officials say the rebels are at least as well armed as they were before last year's heavy fighting. The political shifts in the region, including the leftist Sandinistas' electoral defeat in Nicaragua and Cuba's severe economic difficulties, have not translated into a reduced arms flow to the FMLN, they say.

"We've diversified over the years," Salvador Guerra, a senior rebel commander, said in an interview here. "These changes are not an emergency for us."

Diplomats say that because Central America was flooded with weapons during the upheavals of the 1980s, the FMLN will be able to buy most of the arms it needs on the black market for the foreseeable future. The rebels have received Soviet Bloc arms and equipment through Cuba, Honduras and Nicaragua for years. As the Sandinista army has shrunk by half this year to 40,000 troops, some diplomats believe that the Sandinistas are selling or giving their surplus weapons to the FMLN. However, no evidence of this has emerged.

In addition, some rebel commanders have said -- and diplomats have said they believe -- that the FMLN has been stockpiling surface-to-air missiles, a weapon that was apparently not in the guerrillas' arsenal when they launched the offensive last November.

Army officers and rebel commanders say the FMLN has been operating in relatively large groups of 30 to 100 troops in recent months, an indication that the rebels are ready for heavy fighting. Army units, frequently outnumbered, have been forced at times to avoid combat rather than risk heavy casualties.

However, with the notable exception of Chalatenango province, in the north, where there have been a half dozen or so major clashes since the spring, fighting has not been heavy in recent months. Nor have there been reports of major rebel troop movements toward the capital.

There are indications that any new rebel drive may be different from last year's dramatic attack, in which the FMLN took up positions in residential neighborhoods around the capital. That strategy led to counter-attacks from the army and air force and heavy civilian casualties. Many people blamed the rebels for the destruction of their homes, although there was also anger at the air force for rocketing dwellings.

Guerrilla leaders, without acknowledging their thrust into residential neighborhoods last year to have been in error, say they are not likely to repeat it.

"We've tried to reorient our troops to a more purely military strategy . . . with the least possible impact on the civilian population," said Guerra, the rebel commmander. "The problem is that the main {armed forces} bases are in the capital." In addition to the air force base, San Salvador is the location of other important military and security bases, including the headquarters of the armed forces high command.

There would be further risks for the guerrillas in a new offensive, especially one that involved fighting in the capital. With international attention still focused on the killing by army troops of six Jesuit priests, their housekeeper and her daughter, a new rebel assault could refocus the outrage on the FMLN for provoking more violence.

New fighting could also derail the efforts by Democrats in Congress to cut U.S. military aid to the Salvadoran armed forces. Both houses have passed measures that would slash military aid in half, but the aid would be restored if the rebels launched a major new offensive.

Special correspondent Tom Gibb in San Salvador contributed to this article.