A controversy appears to be developing over the costs of the extensive modifications in the aging Titan II missile system that were recommended in an Air Force study released yesterday.

Gen. Bennie Davis, the Air Force officer in charge of the study, which was triggered by the Titan II explosion that killed an airman last September near Damascus, Ark., said yesterday that it would take "roughly $56 million" to make the 52 remaining intercontinental ballistic missile sites safe for the foreseeable future.

But that figure was immediately challenged by defense specialists on Capitol Hill who called it extremely low.

One House Armed Services Committee staff member, who attended a briefing yesterday by Davis and Air Force Secretary Hans Mark, said he was "shocked" that they would offer that low a figure.

In a press conference later in the afternoon, Davis admitted that neither the Strategic Air Command nor the Air Force had money in their new fiscal 1982 budgets to pay for the major projects the study recommends. He also conceded that over the past few years, funds to support long-term safety modifications in the system had regularly been cut back.

For example, a major oxidizer spill at Rock, Kan., in August 1978 killed two airmen and injured 29. The deaths and many of the injuries attributed to vapor exposures resulted in part from the condition of the safety suits used by technicians handling the deadly propellants used in the missle.

A major recommendation of the Air Force investigation of that accident was that new suits be provided. That recommendation was repeated in another Air Force Titan safety study completed last May. It turned up again yesterday in the Davis study.

The Davis study also recorded, however, that funds to test a new safety suit were cut from the Air Force budget last year again from the current one.

Davis said yesterday that Air Force funding was a "matter of priorities" and he hoped the Titan program would have a new "funding profile."

He said he did not expect all the recommendations to be funded, but at least those "that were most cost-effective."

Among the most costly are: a variety of remote sensing and venting devices to get rid of dangerous fuels and oxidizers that may spill; new vapor detection systems, both those that are fixed in the Titan II silos and portable types that today are not all that reliable; development of an entirely new system to permit the scrubbing, burning or neutralization of fuel and oxidizer vapors within the silo before they are released into the atmosphere; warning systems for each silo to alert civilians living or working nearby; extensive new engineering services to cope with failing Titan parts; a new depot-level mainteance review, and increased reliability testing for the entire Titan system.

Davis reemphasized his conclusion that the Titan system is safe today and would remain so for the forseeable future if the recommended modifications were made.

Asked if he considered it a dangerous situation when, according to his report, the fixed in-silo vapor detection systems are not working 40 percent of the time, Davis responded, "It is not a desirable situation, but it is safe."

He went on to point out that no propellant transfer work is allowed when the fixed system is not working, and that at other times the airmen can carry portable vapor detectors. The study also pointed out, however, that the portable units "sometimes fail or give false alarms."

The portable units, the study adds, have "been programmed for replacement due to nonsupportablility," meaning that because they are no longer made there are no spare parts and they cannot be maintained.