An air Force study newly sent to Congress defends the safety of the aging Titan II intercontinental ballistic missile but asks that extra pay be provided for the technicians who handle the highly toxic liquid fuel used to power the 17-year-old rocket.

The Air Force report was ordered last fall by Congress after 125 fuel leaks occurred at Titan missile sites over five years. One in August 1978 at Rock, Kan., killed two airmen and injured 29.

The study was conducted by Air Force commands who maintain and operate the Titan missiles as well as contractors who built the system and its component parts.

The study found, according to informed sources, that various major and minor modifications and improvements in the Titan and its fuel-handling systems have made it safe to continue in operation for the foreseeable future.

The Air Force, according to the study, currently has under development new "hardware and procedures . . . to control large spills" of the dangerous rocket fuel.

It also is procuring new protective clothing for fuel handlers and "more sensitive vapor detectors."

The Air Force said new teflon seals reduced the number of leaks in the missiles this year, although another one took place at a Kansas site on April 22, as the report was in its final stages.

The study notes that the "current fixed vapor sensing systems" at the Titan sites "will not meet" proposed federal occupational standards for the toxic gas created in a spill or leak.

The Strategic Air Command, the study notes, asked last December for approval to develop a new sensing system.

Extra hazard pay for Titan crews was first proposed by Rep. Daniel Glickman (D-Kan.). Glickman said yesterday he was told by the Pentagon last week that the pay was not needed.

With the study recommending "incentive pay" for fuel handlers, Glickman said there was some confusion and congressional review was needed.

Only 54 Titans exist in the U.S. land-based ICBM force, which is made up primarily of 1,000 more modern, solid-fueled Minuteman missiles. In the 1960s, missile designers turned to the solid fuels because they were safer to handle and more reliable.

In 1967, the Pentagon announced plans to begin retiring the Titan IIs, but that was delayed while diplomats attempted to use them as bargaining chips in strategic arms limitation negotiations.

The Soviets refused to trade against their large missiles, so U.S. policymakers decided to keep the Titans beyond their scheduled 1971 retirement date.

Each Titan II has a single warhead that contains the explosive power of nine megatons (nine million tons) of TNT. That is 750 times larger than the bomb dropped in 1945 on Hiroshima, Japan.

The basic justification for preserving the Titan, according to the study is that it provides a "significant portion" of the ICBM strategic retaliatory force. The 54 Titans with their 486 megatons represent over 30 percent of the entire ICBM force.

Titan warheads are not as accurate as the smaller Minutemen. Thus while the smallers ones are aimed at Soviet missiles, the Titans are aimed essentially at Soviet cities. The study describes the Titan as 'the most efficient large area soft target weapon in the ICBM inventory."

Because the missiles were supposed to be retired in the early 1970s, the Air Force stopped buying new ones in 1967. Thus, today there are only two spares for the 54 in silos, and none has been flight-tested since 1976.

The other major strategic missiles systems in the U.S. force are regularly sampled and flight-tested each year as part of a stringent reliability program.

Nonethless, the Air Force study says 'no trends or apparent limitations" are evident "which would preclude the Titan II from remaining a highly reliable, accurate weapon system through the 1990s."

The report outlines in detail major work that has been done on the Titan to keep it operating well beyond its once-planned 1971 retirement.

Among the most important, according to the study, was a new guidance system, motor switches and flight gyroscopes and launch control set.

Since the Kansas accident, a great deal of effort has been put into changes in handling the rocket propellant.

The nitrogen tetroxide, which fuels the rocket, turns into a reddish gas when released in the air. It combines with liquid in an individual's lungs or on his skin and becomes nitric oxide. In heavier doses it can burn or destroy human cells either inside or outside the body.