The Office of Management and Budget has taken on yet another task for the Reagan administration and become the focal point for its battle against governmental waste and fraud.

According to Edwin L. Harper, OMB's deputy director and chief of the program, the government's despartmental inspectors general have questioned more than $1 billion in costs in the first six months of this year, have recovered $95 million and have saved $300 million that otherwise would have been spent had they not intervened.

Future priorities for the program will be detailed at a press conference today. Reporters will also find that the inspectors general, all of whom were fired by President Reagan in the first weeks of his administration, have been rehabilitated.

"What we're trying to determine is the most cost-effective approach" for the inspectors general in seeking to improve efficiency, save money and stop fraud, Harper said in an interview. "We're a long way from having this locked up."

Candidates for special emphasis include collection debts owed the government and improved management of travel by government employes.

"The key element for inspectors general is not just finding problems, but solving them," Harper said. "The really big dollars are not in fraud, but in program changes."

The biggest obvious change in the program from the Carter to the Reagan administrations is that inspectors general are now meeting at least montly as members of the Presidential Council on Integrity and Efficiency, with Harper as chairman.

That's a comeback for the inspectors general. When they were fired by the new administration, the White House passed the word that it wanted IGs with the attitudes of "junkyard dogs."

The firings "may have been a PR mistake," said Edwin Dale, OMB spokesman. "There was never any intention of subverting" the law requiring most large agencies to have inspectors general.

Twelve of the 15 Carter Administration departmental IGs have been rehired, although most have been shuffled to new agencies to guard against the possiblity they had become too familiar with their old ones to remain genuinely critical.

"We wanted to revitalize the program and give it more support," said Robin Raborn, Dale's deputy.

Early reviews from the IG corps indicate that message has been sent.

Thomas F. McBride is the new IG at the Labor Department, after being fired for "the first time in my life" as the IG at Agriculture. "The closer to the White House" the IG program is, McBride said, "the more effective it will be. . . . Harper is strategically placed."

The challenge, McBride said, "will be to identify the key areas where the most can be saved."

Inspectors general theoretically report to the seretaries of their departments and, in Harper's view, their success depends on their relationship with the secretary. They are also required to submit semiannual reports to Congress detailing their activities. Although those reports pass through the secretary, the secretary can't change them. Now OMB also has a strong hand in the system.

"OMB is clearly part of the landscape," Harper said. "I see the IGs at least once a month; I don't think there's any divided loyalty." Further, he said, OMB is in a position to find additional investigative support for departmental IGs if it is needed.

McBride said, "It does not trouble me to have somebody pull together the government-wide priorities. I still have my statutory responsibility to the Congress." But he can also be fired again by Reagan.

In addition to backing the IGs, Harper said, he also wants to attract support from federal employes in general. Many of them, he said, are convinced "nothing will happen" to wrong-doers and that, therefore, it does no good to report them.

IGs are, by statute, located in 15 departments and agencies. While there are no legislatively mandated IGs in Defense, Treasury, Justice or the Agency for International Development, OMB is considering legislation to change that.

But the problem with having a departmental IG in Defense, Harper said, is that "we don't want people stumbling on something that is closely held," such as the Iranian hostage rescue mission. Under present law, the Secretary of Defense could not discuss an investigation with an IG, so there must be some way to call off the junkyard dogs if they are to be placed in the Pentagon.

IGs are not loved by their agencies. Says McBride at Labor: "My initial impression is that there is a strong wish we'd go away.