SAN JOSE, COSTA RICA, SEPT. 8 -- A top Salvadoran rebel commander said last night that the guerrillas "never will" lay down their arms and will pick up the pace of fighting in coming months, despite a peace plan signed by the five Central American presidents that calls for a cease-fire to take effect throughout the region on Nov. 7.

Shafik Handal, one of five leaders of the rebel Farabundo Marti National Liberation Front (FMLN), said: "We're not about to lay down our arms now and we never will."

It was the first interview with a member of the leftist guerrillas' elusive military command since the pact was signed Aug. 7 in Guatemala. According to Handal, the guerrillas have not softened their longstanding demand for a share of power and view the peace accord as "a formula for our surrender." Last month, Guillermo Ungo of the rebels' political arm also expressed pessimism regarding the peace plan.

The plan, based on a proposal by Costa Rican President Oscar Arias, calls for a cease-fire, amnesty to allow guerrillas to renounce armed warfare and specific steps toward full pluralistic democracy. All measures are to take effect Nov. 7.

Salvadoran President Jose Napoleon Duarte, who has been Washington's most consistent ally in Central America, appeared to distance himself from the Reagan administration by signing the pact, which Washington has welcomed but also criticized. Duarte has pointed out that the pact isolates the guerrillas politically and cuts off any assistance from Marxist countries.

Duarte "wants to go hunting for a caged lion," Handal charged. "It is absurd to ask us to give up after seven years of civil war."

The FMLN does not reject the accord entirely but sees it as a jumping-off point to renew a peace dialogue with the Salvadoran government, Handal said. He accused Duarte of trying to roll back the few results of talks in 1984 that collapsed after two rounds.

"We have one responsibility under this pact: to remain open to a dialogue that will lead to a negotiated settlement," Handal said. He reiterated past FMLN proposals for a transition government that would include their leaders and permit some of their fighters to remain armed.

In mid-August, Duarte proposed a meeting with the rebels Sept. 15. The rebels accepted, but Duarte said they would have to accept all terms of the peace plan for the talks to go forward. The plan only requires Duarte to talk with his opposition that is not under arms.

Handal made a rare public appearance with other rebel leaders in San Jose after conferring for two hours yesterday with Arias, who agreed to mediate between them and Duarte. Arias said there remain "rocks and barriers" in the path to the talks and doubted that they could be swept aside by Sept. 15.

The portly, gray-bearded comandante said the guerrillas do not plan any measures to comply with clauses of the plan banning outside aid to rebels and the use of any nation's territory by guerrilla armies. He denied that his fighters receive substantial amounts of Soviet Bloc aid.

Since 1980, the FMLN has captured more than 7,000 rifles and 400 artillery pieces from the Army to outfit its 6,000 troops, he said, adding that it also relies heavily on on homemade mines, traps and explosives. He asserted that U.S. aerial surveillance of guerrilla zones is so thorough that it precludes moving large shipments of arms.

Nicaraguan President Daniel Ortega admitted earlier this year that some arms for the Salvadoran guerrillas pass through Nicaragua, but he said it was not done as a matter of government policy.

At 56, Communist Party chief Handal is the eldest of the five rebel commanders, a veteran of three decades of bitter political battles. He is believed to spend much of his time traveling on missions to bolster the FMLN's Soviet Bloc ties.

Handal said the FMLN will accelerate its warfare this year in response to what it sees as a growing U.S. involvement in the war. His guerrilla forces have become skilled in moving in small groups, coming together for assaults on Army targets, then scattering quickly, he said.

He said that former CIA director William Casey and senior White House officials arranged a meeting with guerrilla leaders in February 1981, a few weeks after President Reagan took office, in a Latin American embassy in Washington.

As the rebels were winging their way toward Washington aboard a plane provided by the Latin government, the White House abruptly canceled the talks, he said.

In recent weeks, Enrique Bermudez, the top commander of the Nicaraguan rebels, known as contras, also rejected the peace plan's call for an amnesty.