The Reagan administration yesterday declared that the air traffic controllers' strike was over, and announced that 230 applicants already have been hired to replace fired controllers.

Transportation Secretary Drew Lewis, using the past tense in referring to the 5-day-old strike, said: "We're forgetting about the strike that did exist, and we're going ahead in terms of hiring people and figuring out how we operate" the nation's air traffic control system with reduced staffing "in the next six months to a year and a half."

Hiring commitments have been made to 91 additional controller applicants, "and we're receiving phone calls at the rate of 5,000 a day from people who would like to be considered applicants for this job," Lewis said.

The 61-nation International Federation of Air Traffic Controllers Associations, meanwhile, urged its members not to clear flights into U.S. airports, saying the strike had created a "situation which we know to be unsafe." (Details on Page A18)

About 12,000 of 13,000 striking controllers ignored President Reagan's work-or-be-fired deadline Wednesday. Yesterday, Lewis repeated his statement that strikers who disobeyed the president's order can consider themselves fired.

"I regret that that's the position I'm in. But that's where I am," he said.

The government's one apparent concession to the strikers was Lewis' public statement yesterday that "nothing is to be gained" by putting or keeping any of the controllers in jail. Five striking members of the Professional Air Traffic Controllers Organization were arrested this week, and there was much speculation that PATCO President Robert E. Poli also would be imprisoned.

"It's my recommendation that we not do that," said Lewis, who added that the final disposition of any legal actions is up to the Justice Department.

Lewis said the point is that all striking controllers who cannot prove that they were intimidated or otherwise forced to walk off their jobs are fired. The controllers have about a week to respond to the thousands of dismissal notices that began going out to them Wednesday. Asked if there would be any leniency or amnesty in the case of dismissed strikers, Lewis said flatly, "No."

U.S. District Court Judge Oren Lewis in Alexandria also said no yesterday to five PATCO leaders who asked to be taken out of contempt of court. The five, including Steven L. Wallaert, who has been in Fairfax County jail since Wednesday, had refused Lewis' order to end their role in the strike.

Lawyers for PATCO officials argued yesterday that their clients technically are no longer employed by the federal government, and could not go back to work, as the judge ordered, "even if they wanted to."

Air traffic control supervisors from Washington National and other airports who were called as witnesses testifed that they have received no official word from Lewis that the strikers had been fired, and refused to say whether the seven-day dismissal notices mailed by the government were final.

After the arguments, Judge Lewis said his orders were still being disobeyed and he refused to lift his contempt ruling.

But in Chicago, a federal judge threw out contempt findings and $756,000 in fines against two locals and eight officials. "I cannot hold an individual in contempt . . . for not returning to work if the employer won't take the person back," U.S. District Court Judge Marvin Aspen said.

PATCO President Poli, still maintaining that his striking members were "holding firm," called the actions taken by Judge Lewis and other federal law officials in connection with the strike "insensitive, fascist tactics." As he has in the past several days, Poli insisted that his members will continue the strike that the government says no longer exists.

Lewis and Federal Aviation Administrator J. Lynn Helms said again yesterday that about three-quarters of all 14,200 daily scheduled commercial flights were operating with few delays, despite the strike, which began Monday.

Helms also denied allegations that the FAA has been overworking supervisors and nonstriking controllers, thereby endangering travelers. "Basically, our program is working well," Helms said. "We have now absorbed the impact of the big event."

On that point, he was supported by a group that could have been allied with PATCO -- the Air Line Pilots Association. "I can assure you that ALPA has continued to monitor the safety conditions since the beginning of the strike," said ALPA President J. J. O'Donnell. "So long as airline pilots continue to fly their appionted routes, the public can be assured that it is safe for them to do likewise."

Meanwhile, the government yesterday went about beefing up its air controller training courses at the FAA Academy in Oklahome City, closing, temporarily, more than 50 smaller airports until controller manpower can be increased, and positioning about 2,000 military controllers until the new civilian controllers come aboard.