If there were ever any doubts about what is to be gained by the four-city "truth squad" blitz under way by a conservative coalition of Senate and House opponents of the Panama Canal treaties. Sen. Paul D. Laxalt (R-Nev.) inadvertently dispelled them when the journey was barely five minutes old.

As the principals of the $80,000 whirlwind lobbying effort gathered at National Airport for a kickoff press conference Tuesday, Laxalt scurried about, prodding the group closer together like an anxious teacher composing a class photograph.

"Can you all shift over slightly so we can get it better framed?" he asked, carefully eyeing the positions of the waiting television cameras.

From start to finish, the Eastern and Midwestern leg of the four-day, 6,500-mile campaign had all the markings of a slickly packaged media spectacle, notwithstanding logistical nightmares caused by blustering snowstorms and the funeral of Minnesota Sen. Hubert H. Humphrey, which forced the sponsors to cut the trip nearly in half.

But the surest proof of the trip's worth to the treaties' opponents was the smile spread across Laxalt's face when he walked into a Miami hotel and saw seven television cameras being readied for a rally, and the same joyful look eight hours later when an aide informed him that the "truth squad" had made sizable play on the three television networks in its first day on the road.

"The fact is, 80,000 bucks would be a few minutes' television time, if you could buy it at that price. The administration has been preaching pure propaganda at the taxpayers' expense, and now it's our turn to speak, at our own expense," Laxalt said in an interview. Along with Rep. Philip M. Crane (R-Ill.), he arranged the blitz to counter pro-treaty speaking tours by administration officials, including Secretary of State Cyrus R. Vance.

But, according to its backers, the anti-treaty trip had another, more purposeful aspect, which became clear at the first of four public meetings.

A questioner among 250 people gathered at the Marriott Airport Hotel in Miami asked, "What can we do to convince Stone and Chiles to vote against the treaties?" He was referring to Florida's two Democratic senators, Lawton Chiles and Richard Stone, who are uncommitted on the canal issue.

Laxalt suggested writing letters that call attention to the ideological alliance between Cuban President Fidel Castro and Gen. Omar Torrijos, Panama's military leader.

"We hope that they [Lawton and Chiles] are not locked in place," he added.

Elaborating later aboard the squad's chartered DC-9, Laxalt said, "Some senators like the best of both worlds, and the amendments being suggested offer that kind of vehicle."

He was referring to the proposed treaty changes that would guarantee the United States the right to defend the neutrality of the canal with military force, and assure priority passage to U.S. warships in an emergency.

"The only amendment acceptable to us is removal of sovereignty," he added, meaning full U.S. control of the security of the waterway.

"Anyone running for office this year - and even in 1980 - has a tough political decision to make. The closer we get to the primaries, the tougher it will be for those up for re-election to vote for the treaties."

Asked whether the issue has been defused by Minority Leader Howard H. Baker Jr.'s cautious support of modified versions of the treaties, Laxalt said, "In a normal issue, the position of the leadership is very important, I will concede that. But this is not a normal issue. People are going to have to make decisions individually."

Rep. Mickey Edwards (R-Okla.), another "truth squad" member, suggested that conservatives made a "tactical error" by identifying Baker as a key factor in rejection of the treaties.

"His statements can be interpreted as a severe blow to our cause, but I don't believe that at all," Edwards said. "The leadership won't be crucial, but public opinion pressure will."

A dozen senators, representatives and national defense "expert witnesses," including several retired military officers, boarded the $10,000-a-day chartered jetliner with about 30 reporters for the Eastern portion of the trip. On Thursday, former California Gov. Ronald Reagan is scheduled to join the entourage in Denver, after which the group will travel to Portland, returning Saturday.

Scheduled visits to Nashville and Atlanta were scratched Monday because of Humphrey's death, and a severe snowstorm in the Midwest forced the group to eliminate Cincinnati, a key city because of its vast television market.

Cincinnati television is beamed to Ohio, Kentucky and West Virginia, Laxalt noted - coal-producing areas where the canal's future is of concern because of coal shipments to Japan. While Senate Majority Leader Robert C. Byrd of West Virginia and Sen. Howard M. Metzenbaum (D-Ohio) favor approval of the treaties, most of the remaining senators in the three states are not yet committed.

The squad's sponsors said the blitz has been organized like a major political campaign, with specially targeted media markets, advance teams and carefully arranged "public receptions."

The group is planning a smaller blitz next month, in which it will visit Cincinnati and Nashville, and perhaps a third city.

Crowds in the first portion of the trip were generally small and partisan - 250 people in Miami, many from veterans organizations and conservative groups - but that did not seem to concern the sponsors.

"To some extent, we're preaching to the choir, but hopefully every one of them will be a messenger of what we're saying," Laxalt said.

Some of the leaders expressed continued bitterness with the Republican National Committee, which, at the direction of Chairman Bill Brock, refused to release $50,000 to the blitz campaign from an estimated $700,000 collected by a fund-raising letter signed by Reagan. Howard Phillips, executive director of the Conservative Caucus, said the money was intended to be used to defeat the treaties, and that his group is considering a lawsuit against the RNC.

So far, the American Conservative Union has spent more than $600,000 on the canal issue, some of it for a 30-minute film and a videotaped editorial.

Conservative fund-raiser Richard A. Viguerie, who accompanied the squad as far as St. Louis, arranged a mail solicitation of 1.8 million letters.