Salvadoran guerrilla forces have in large measure pulled back to remote strongholds along the mountainous Honduran border to avoid the U.S.-supported Salvadoran Army engaged in its most sustained and aggressive campaign since last summer.

The rebel pullback, now in its third month, has generated a debate over whether guerrilla leaders have staggered backward under recent Army attacks or simply faded away for the moment to wait, in classic guerrilla fashion, for the right time and place to mount a counterblow.

Salvadoran and U.S. officials are portraying the relative calm as a rebel retreat in the face of new vigor in the Salvadoran Army, bolstered by a new defense minister and U.S. guidance emphasizing civic action rather than the one-shot sweeps traditionally favored by Salvadoran officers.

The guerrilla pullback, in this view, has been accompanied by increased willingness among the rebels' backers and advisers in Cuba and Nicaragua to negotiate under pressure of the Reagan administration's display of resolve and military power in Central America.

Several signs buttress these claims being advanced by the Salvadoran military and U.S. officials here and in Washington. Most telling, perhaps, is the lack of a guerrilla counterattack against the National Plan that has saturated the provinces of San Vicente and Usulutan with 5,000 soldiers and dozens of reconstruction projects since the first week in June.

Others, less conclusive but heartening to U.S. advisers here, include appeals for guerrilla volunteers broadcast over the rebels' official Radio Venceremos in recent days, possibly indicating a manpower shortage in the Farabundo Marti National Liberation Front, the overall guerrilla military organization.

On a smaller but still vivid scale, a guerrilla team attacked a bank Tuesday at Jucuapa in eastern Usulutan, seeking funds for the revolution, but was beaten back without a centavo by an Army unit that rushed in from neighboring San Miguel province.

According to an Army report, the operation had a Butch Cassidy quality, with guerrillas bursting into the bank but proving unable to blast open the safe before being forced to flee by the advancing soldiers.

Guerrillas and their leaders, however, have a very different explanation for the recent rebel quiescence. The front's five guerrilla groups are absorbing an unprecedented influx of recruits and arms gathered during the eight months of guerrilla successes that preceded the present calm, they say.

"The guerrilla movement is in this stage like a boa constrictor that has swallowed a calf," said an official of the Democratic Revolutionary Front, the guerrillas' political arm. "It is digesting."

The guerrilla radio said five days ago that since January alone, rebel forces have captured 1,826 rifles "sent by Reagan" to the Salvadoran Army, along with 99 heavier weapons including mortars, machine guns and light artillery. Assuming, as reported by U.S. sources, that 6,000 men already were armed, that would mean guerrilla forces have enough arms for a 30 percent increase in manpower.

A guerrilla column leader calling himself Antonio said in an interview in rebel-held northern Morazan province that his organization is "incorporating" more recruits than ever before. The lack of response to Army pushes in San Vicente, he asserted, means only that the guerrilla leadership is adjusting its tactics in anticipation of a counterattack at an opportune time.

"The tactics of guerrillas are to attack the enemy where they want, and when they want, not when the enemy wants," he said.

Antonio, 23, wore a camouflage uniform and a red bandana marked "ERP," Spanish initials for his group, the People's Revolutionary Army. ERP irregulars and locally recruited militiamen carrying M16, G3 and FAL automatic rifles were manning a checkpoint on the road running north from San Francisco Gotera toward Perquin.

Chief of what he said was a 160-man column, Antonio said the entire north of Morazan province--all territory north of the Torola River--was uncontested guerrilla territory. A visit to the area, possible only by fording the river since guerrillas blew out the only bridge last spring, showed no signs of Army presence and no hesitation by guerrilla troops to drive around openly in their diesel-powered Japanese trucks.

The remote mountains of Chalatenango province, according to guerrilla accounts and reports here in the capital, also contain unmolested rebel units. The northern stretches of both provinces traditionally have been guerrilla redoubts only rarely troubled by Army attacks.

During the past eight months, guerrillas had ventured afield with only sporadic resistance from the Army even outside their strongholds. The Chalatenango town of La Palma, for example, was run openly by guerrillas for several months until Army forces reestablished a post there last month without resistance from the guerrillas.

In some ways, the present shift of fortunes is simply another stage of a cycle that has been recurring ever since the civil war began here nearly four years ago.

Ten months ago, for example, Thomas O. Enders, then U.S. assistant secretary of state for inter-American affairs, claimed in a speech prepared for the Inter-American Press Association in Chicago that the Salvadoran rebels "can no longer hope to win the war" because the Army was "better equipped and organized and has learned to fight in the field."

By this spring, however, Enders was no loner in the administration, and his former colleagues were expressing fear that unless emergency aid and training were rushed to the same Army, it risked losing after all because it was not fighting in the field.

The conflict appears at this stage to have settled into another phase in which the Army is doing better and the guerrillas are pausing, giving rise to another round of encouraging remarks in Washington.

Conversations with Salvadoran officers and guerrillas in the field indicate that it is difficult to judge whether this time the Army-up phase can be made to last. The San Vicente operation has been going on only for two months. It is too early to judge the staying power of its civic action goals, therefore, and too early to write off the possibility of a guerrilla counterattack that would disrupt progress made so far.

Col. Rinaldo Golcher, who commands the San Vicente and Usulutan National Plan, told reporters last week that some guerrillas appear to be filtering back into the area. One quick clash left 11 of his troops dead, he acknowledged, and he and his U.S. advisers are on the alert for more such attacks.

Local authorities say that the guerrillas never really left the area altogether, but rather backed off into remote corners of the countryside. In Berlin, the Usulutan city where former U.S. ambassador Deane Hinton presided at a major reconstruction project announcement in the spring, for example, residents are still afraid to take the road down the mountain toward San Augustin.

"No one goes that way," said a national policeman guarding the Berlin bank. "Sometimes you run into one or two, sometimes you don't. It is just a matter of luck."