The president of the Professional Air Traffic Controllers Organization acknowledged yesterday that he misjudged the Reagan administration's resolve to retaliate when he pulled 13,000 of his members out on nationwide strike.

"We could be accused of miscalculation," Poli said yesterday in an interview on a Cable News Network program, "Newsmaker Saturday."

"I was surprised. . . . I didn't really believe that they would have taken such harsh actions," Poli said.

The strike, which began Monday, has resulted in jailings, heavy fines and the firing of thousands of controllers who refuse to return to work.

The Federal Aviation Administration reported yesterday that 78 percent of scheduled commercial flights were operating close to schedule.

The union leader said his miscalculation stemmed from an "understanding" he thought he had with presidential candidate Ronald Reagan that a Reagan administration would support controllers' demands for improved working conditions. That understanding led PATCO to break ranks with most of organized labor and endorse Reagan last year, a point which also figures in the rest of organized labor's tepid response to PATCO's plight.

"We endorsed Ronald Reagan because of his sympathy and feeling toward the air traffic control system," Poli said yesterday. The union leader had met with Reagan in Tampa, Fla., on Oct. 20, 1980. Reagan was understanding, expressing concern about reports that the nation's controllers were working under unwarranted stress, Poli said.

That same day, after discussing the union chief's concerns with members of his campaign staff, Reagan sent a letter to Poli that said in part:

"I have been thoroughly briefed by members of my staff as to the deplorable state of our nation's air traffic control system. They have told me that few people working unreasonable hours with obsolete equipment has placed the nation's air travelers in unwarranted danger. . . .

"You can rest assured that if I am elected president, I will take whatever steps are necessary to provide our air traffic controllers with the most modern equipment available and to adjust staff levels and work days so that they are commensurate with achieving a maximum degree of public safety."

Poli said yesterday that he understood that to mean that candidate Reagan endorsed PATCO's push for a shorter workweek and other measures that the government later said were too expensive.

Conversations with administration officials after Reagan was elected, particularly with Transportation Secretary Drew Lewis, reinforced his belief that the administration was on PATCO's side, Poli said.

"During those times, I was told "We will address these issues,'" Poli said.

But Poli said that as the administration began to design and push its spending-cut and tax-cut plans through Congress, the tone began to change. After the assassination attempt on Reagan March 30, the administration became even preoccupied with its own problems. Poli said.

He said Lewis told him: "'Bob, don't press the issue right now . . . . Please, can't you keep your union intact? We know your contract expired [March 15], but we're going to get to you.'"

Poli said he blames Lewis for "breaking a commitment" that he thought the administration had made to his union.

"From the time after" Reagan was elected until the beginning of negotiations in February, "I was talking to Drew Lewis," Poli said. "It was his responsibility, it was his problem, and he's the one who has ill-advised the president" in the administration's dealings with PATCO and its handling of the strike, Poli said.

An aide to Lewis yesterday denied that charge.

The aide, who did not wish to be identified, acknowledged that Poli and Lewis had spoken before contract talks began. But the aide said Lewis acted in good faith and it was Poli who had broken his commitment to the administration.

"They were told that they were going to get something [in a new contract], and they did get it," the aide said. "They got twice what any other federal employe got."

The union sought a $1.2 billion wage and benefits package that included a $10,000 annual pay increase for controllers, who now average $33,000 a year.

The government offered a $40 million package that would have increased controller pay and benefits by 6.6 percent, or about $3,000 a year. That increase would have been in addition to a 4.8 increase wage increase due all federal employes.

Poli accepted the government's first offer June 22. He said it was "fair," but his membership overwhelmingly rejected it one month later.

The aide to Lewis yesterday accused Poli of "working against the contract" he signed June 22.

"He even got up and shook Drew's hand, and then he went out and told his members to turn it down," the aide said.

Poli denied that charge yesterday, and he repeated his now-familiar claim that his 12,000-plus striking members were "solid" in their resolve to keep their picket lines up.

A federal judge in Kansas City, Kan., yesterday ordered four PATCO members released from jail, ruling that since they had been fired they no longer could be held in contempt for refusing to return to work.

The Federal Aviation Administration reported yesterday that 78 percent of the nation's 14,200 daily scheduled commercial flights were operating close to schedule. The government still was churning out dismissal notices to strikers, and the FAA had hired 321 people to begin training to replace the strikers.