Secretary of State Cyrus R. Vance finish his speech calling for approval of the Panama Canal treaties. Then he told the 500 people gathered in a Charleston, W. Va., college auditorium: "I'll be happy to answer any questions."

First on his feet was a man who gave his name as Maloney. He asked: "What was your name again? Lance?"

After the embassassed snickering subsided, others in the audience at Charleston's Morris Harvey College Thursday night identified Maloney as a local character noted for running unsuccessfully for political office and asking fuzzy questions at public gatherings.

But as Vance was to discover several more times that night - and again on the following day in Louisville and New Orleans - the Panama Canal is a subject that provokes some of the strongest and most frustrating questions ever raised in an American political debate.

The battle is expected to begin in the Senate next month over the Carter administration's proposal to surrender U.S. control of thecanal by the end of the century. The administration faces an uphill struggle to wrest the required two-thirds vote from a deeply divided Senate, and this week it began deploying its biggest guns for the softening up process.

First came Vance, who temporarily deserted his State Department desk to swing through West Virginia. Kentucky and Louisiana on a two-day foray of speech-making and handshaking. In the days ahead, several other top-echoen administration figures will fan out across the country, and President Carter will devote a televisied "fireside chat" to the canal issue.

Their purpose to coax public opinion in those states where the canal arouses special passions into support of the treaties. The administration hopes that a shift in voter sentiment will put pressure on wavering senators in the targeted states and bring them into the pro-treaty column.

It's going to be a noisy battle - one that will see the administration's spokesmen contesting for voter support with the "truth squads" that the dedicated and well-organized antitreaty forces will be throwing into the fight during the next few days.

As a preliminary psychological warfare fambit, the antis have been portraying themselves as David facing the Goliath-like power of an opponent armed with all the resources of the presidency.

If the Vance trip this week was an example, though, it seems to stand that comparison on its head.

The truth squads - a Who's Who of conservative congressmen and retired military brass - will be whizzing around the country in chartered jets. By contrast, Vance found that, for the first two legs of his tour, the Defense Department was able to provide him only with a 1952-vintage, propeller-driven, two-engine Navy Convair that chugged through the air at roughly half thespeed of a jet.

His plane might have been a symbol of what many political pulse-takers say is the problem with the administration's treaty-selling campaign - too modest and too slow moving to cover the ground in the short time that remains.

That the administration still has a lot of selling to do was made clear by the questions Vance heard along his way.

Some had no relevancet o the Panama issue or, indeed, to anything else. There was an intense young man who asked how many abortions had been paid for by the Rockfeller Foundation, which Vance formerly headed. Another left the secretary scratching his head in puzzlement over an incoherent proposition that seemed to equate U.S. control over the canal with recognition of Communist China.

Most questions, of course, did relate to the canal controversy. But even there, a high percentage of them showed clearly that many people still view the treaties through a prism of suspicion, fear, and almost total ignorance of what they say.

Everywhere, there were demands to know why Panama shouldn't be required to pay the United States for the canal.Or, more simply, why there is any need to give up the canal at all.

Perhaps the most frequently asked question was whether Panama's military leader, Gen. Omar Torrijos, is a Communist and ally of Cuba's Fidel Castro. If so, people ask repeatedly, wouldn't a U.S. withdrawal from the canal result in another Vietnam "with the Reds moving in behind us to take over?"

Vance's responses didn't exactly dazzle anyone with falshes of ringing rhetoric. Instead, he took the calm, reasoned approach that sometimes causes correspondents covering the State Department to refer to him as "Cyrus the Gray."

His answers were throughtful and factual. But standing before audiences in his gray or dark pin stripe suits, he seemed every inch what he was before joining the administration - a Wall Street lawyer arguing a complex case before a judge rather than someone trying to play on the emotions of his listeners.

Once or twice, he came close to stumbling. In New Orleans, where everyone seems preoccupied with Sunday's Super Bowl game between Dallas and Denver, the first question asked of Vance at a Chamber of Commerce dinner was to "pick a winner Sunday."

With a puzzled frown, Vance turned to the man sitting next to him on the dais with whispered, "What's Sunday?"

However, once he got the word, he managed a quick recovery and turned aside the audiency's titters by shooting back: "I predict the winner's initial will begin wiht 'D.'"

He had other bright moments - perhaps most noticeably in Charleston when, after the formal program, Vance perched on the edge of the auditorium stage to sign autographs for students and chat with them about foreign policy and the opportunities for careers in the Foreign Service.

Mostly, though, he chipped patiently away at the questions. No, Torrijos is not a Communist. Yes, the United States would intervene forcefully against any threat against the canal. No, the threat won't mean a second Vietnam. Yes, they will further American military and economic interests and gain respect for the United States throughout Latin America.

Again and again, he reiterated his main theme: "I think it's important that we ensure that people have the facts. When they have the facts, it is my judgment that there will be sufficient votes for these treaties."

It was a soft tell quite different from the rhetorical drum rolls and passionate thunderclaps that the "truth squads" will be unleashing on the other side. Then, after each has had its say, the Senate will have to decide which side chose the winning strategy.