The arms flow to leftist guerrillas in El Salvador appears to have increased dramatically in recent months.
According to United States Ambassador Deane R. Hinton, the flow is now ''at an all-time high.''
Included are arms and ammunition, radio and other communication gear, and medical supplies.
The arms comes in over rugged mountain trails, sometimes on mule-back, from Honduras; by air drops in the remote and rugged guerrilla-infested northern reaches of the country; and aboard small boats and even canoes plying the waters of the Gulf of Fonseca and the smooth coastal waters of the Pacific.
''It is as if you had 40 or 50 Ho Chi Minh trails,'' comments one observer close to the story.
That reference to the Ho Chi Minh trail that supplied communist guerrillas in South Vietnam during the 1960s with their arms, ammunition, and equipment is not mere hyperbole, say these sources. They say it is an accurate comparison to the many routes used by communist guerrillas more than a decade ago in Vietnam.
The amount of arms and equipment flowing into El Salvador can at best be only a guess. But based on data from observations by Salvadorans on the ground and from sophisticated monitoring equipment, the flow is more than enough to supply the approximately 5,000 guerrillas operating in virtually every part of this Massachusetts-size nation.
Observers here, echoing the Reagan administration's statements on the subject , say that Nicaragua serves as the staging area for much of the flow. But these sources are more concerned with the flow itself and its routes, than with the actual origin of the equipment. Some of the flow is stopped by Salvadoran Army and security forces. But it is thought that the vast majority is slipping through.
Nicaraguan officials, it should be noted, deny they are supplying arms to Salvadoran guerrillas.
Among materiel captured entering the country and picked up after encounters with the guerrillas is a good deal of quite sophisticated radio and other communications equipment.
There are also vast quantities of arms and ammunition. The arms include small sidearms, rifles, machine guns, antiaircraft guns, rocket-propelled grenades, M- 79 grenade launchers, and antitank weapons. The latter, together with the rocket-propelled grenades, have a capability of knocking out tanks with their tremendous penetrating power.