The Salvadoran armed forces are faced with significant shortages of manpower and materiel in their efforts to thwart an announced guerrilla offensive designed to keep national elections from taking place in two weeks, according to top Army commanders here.

The commanders say they are depending mainly on the will of the Salvadoran people to overcome intimidation by the guerrillas now but that over the long stretch they will have to greatly expand their forces to win the war.

In obvious frustration, these officers also return again and again to what they see as a need for vastly increased American aid--enough to train and supply a doubling of the combined Salvadoran armed forces from about 25,000 men to 50,000. They did not specify the time frame but said that ideally they would like to double the armed forces within a year.

The officers cited increasing flows of arms to guerrillas as a factor in their need for increased help from the United States.

"The amount of aid we've received is still insignificant," said Gen. Jaime Abdul Gutierrez, Salvadoran vice president and commander in chief. In response to questioning about the American role in El Salvador, Gutierrez said, with an ironic smile: "Some people here said the United States is keeping us like prisoners in a Nazi camp, giving us enough to keep us alive but not much more." Gutierrez did not say whether he accepted that viewpoint.

Washington has supplied $80 million worth of regular and emergency military aid here since October.

Gutierrez, the only member of the original junta formed after the October 1979 coup who remains in the government, did not say how much a doubling of the armed forces would cost. He said he does not have "the least idea" of the monetary cost of the war to date.

Gutierrez blamed many of his Army's problems on the guerrillas outside training and supply. He said, without giving evidence, that as many as 200 Salvadoran insurgents trained in other countries have returned to fight here in the last few months.

While Gutierrez talked of the need to double the armed forces mainly in terms of the conflict inside this country's borders, a regular army of 50,000 would also give El Salvador the largest military force in Central America.

Gutierrez charged that Nicaragua is "definitely" the source of much guerrilla support and the regional problem of what he considers Soviet expansionism.

"If the source is not neutralized," said Gutierrez, "we will have the problem for a long, long time."

The immediate concern of Gutierrez and other senior officers, however, is the March 28 elections.

Ferman Cienfuegos, one of the five top commanders of the insurgent forces, said last week that on election day a "popular uprising" will be called and "there will be no public transport. In addition, there will certainly be no electricity in the country, business will have to come to a stop, there will be no traffic on the highways and we will have encircled several of the nation's cities."

Senior officers in the government forces say they are confident that the guerrillas do not have enough popular support to mount a full-scale insurrection and are attempting to intimidate Salvadoran voters while telling the world that any low turnout that occurs as a result of this intimidation is proof of support for the insurgents.

But these same officers say that if current, relatively small counteroffensives do not work there is little they can do to keep the insurgents from carrying out their plans to disrupt the election.

"When a bridge is destroyed, yes, for at least a few days that highway is paralyzed," said Deputy Defense Minister Francisco Adolfo Castillo. "When an electric energy tower is knocked down the electrical energy is cut--that part, yes, you have to recognize what they can do, because they've done it before."

Castillo said, "We are trying within our capabilities" to avoid the threatened paralysis of the country. He said people will not have to travel long distances to vote and that electricity is not needed in the process.

"You will see a very significant thing happening that day," Castillo said. "The people, despite everything, will vote."

Castillo said that, militarily, "to be able to have better control we would have to have a much bigger and better equipped armed forces, possibly double what we have now."

Part of the problem, Castillo said, is that no matter whether the guerrillas have the popular support they claim, they present a large and threatening military force.

Castillo estimates that the insurgents have at least 5,000 armed and seasoned combatants and 10,000 or more militia that could be given arms in the event of a major offensive. Castillo said he believes that the guerrillas have enough arms now to equip the militias but have not done so because they do not trust them.

Most armies hope to have a 10-to-1 numerical superiority over insurgents in any guerrilla war, and even at present levels that ratio is no better than 5-to-1 here.

If the size of the armed forces could be doubled within a year, Castillo said, "that would be ideal," bringing the size of the armed forces to about 1 percent of the population.

Speaking strictly in military terms, Castillo said, it would be best to have more than the current limit of 55 U.S. advisers here, an expansion of the $15 million training program for Salvadoran troops in the United States and increased training for Salvadoran officers.

Gutierrez sees the March 28 elections as a vital step not only in the democratization of the country but in this effort to create and supply a much bigger army.

El Salvador has found itself increasingly isolated by international political pressures from arms suppliers it previously used, according to Gutierrez.

He specifically cited difficulties in obtaining spare parts and armaments for the old French-manufactured jets that form the core of El Salvador's small conventional air force. Gutierrez also said that the West German G3 rifles that are standard issue for 75 percent of the armed forces are in need of spare parts and muzzle-launched grenades that the West Germans, who sold the guns to El Salvador more than a decade ago, now will not supply. About 25 percent of the armed forces are now armed with American M16s.

Gutierrez is also aware that one of the primary obstacles to what he sees as sufficiently increased aid from the United States is popular and congressional opposition to his government.

"This is a political war and we urgently need more ample international recognition," Gutierrez said, noting economic and social as well as military problems. "We believe the elections give us more legitimacy."

The guerrillas repeatedly have said they would not participate in the election, recognize its results or allow it to take place if they could help it.

Instead, the guerrillas have offered to negotiate with the government. Both the Salvadoran government and the Reagan administration have rejected these initiatives with the argument that negotiations would give the "leftist minority" a share of power it cannot win on the battlefield or earn at the ballot box.

The guerrillas now seem to be intent on an effort to force the Salvadoran government into a position where it will have to negotiate with them, but Gutierrez ruled out any such talks even as a tactic to undermine the most extreme Marxist factions of the insurgents.

"Nobody who sits down with the communists to negotiate has beaten them," said Gutierrez. "I don't think there is a possibility of getting peace just by sitting down at the table."

"Our point of view is that the power resides in the people," Gutierrez said.