For several years, the 54 aging, giant Titan II missiles have been major accidents waiting to happen.

Before yesterday, two airmen had been killed and nearly 80 injured, some seriously, as the result of leaks in the missile's fuel and propulsion systems and other accidents.

In addition, there have been hundreds of small incidents in the last five years, most of them unreported to the public, and a number of close calls.

In August 1979, for example, a metal rod dropped on an electric circuit breaker in a Titan silo near Heber Springs Ark., causing a fire. While the flames were being extinguished, the oxidizer and fuel in the missile heated up, creating great pressure.

According to a senior technician there, "Only great skill kept that missile from exploding." Unlike rural Damascus, site of yesterday's accident, Heber Springs is located in a populated area.

The Heber Springs incident and nine other leaks and accidents at Arkansas Titan sites since March 1979 became public only last month. They were contained in a list the Air Force turned over in response to requests from Sen. David Pryor (D-Ark.), The Washington Post and network news producer Robert Lissit.

Last January, responding to similar requests from Kansas congressmen, the Air Force disclosed there had been 125 incidents between 1975 and 1979 at Titan sites in Arkansas, Arizona and Kansas.

The Titan II was the first tested in 1961 and by December 1963 the three Titan squadrons totaling 54 missiles were declared operational.

With a nine-megathon warhead -- TNT -- it was more than 700 times more powerful than the Hiroshima bomb. The purpose of the Titan II warhead was to threaten enemy cities. Initially it was aimed, for the most part, at targets on Mainland China.

Originally designed for 10 years of service, the Titans were scheduled to be retired beginning in 1971. The Pentagon wanted to get away from their dangerous liquid propellants in favor of the safer solid-fueled Minuteman.

The Titans, however, have remained operational for more than 18 years, a bitter reminder of Henry Kissinger's unsuccessful attempt to trade them away during the 1972 SALT I negotiations.

Kissinger offered the Titans as a sacrifice to get the Soviets to reduce the number of their giant SS9 missiles. The deal failed, and the Titans have remained in America's arsenal since.

In recent years, however, the Air Force Strategic Air Command began to run out of parts for the complex missile system. And since the Johnson administration had planned to retire them, no additional missiles were bought, the normal backup missiles had been used up and reliability test firings had to be stopped.

During its normal lifetime, the missile occasionally began to leak the highly volatile liquid fuel and oxidizer that is used to ignite the fuel.

Beginning in 1978, however, as the aging fuel system seals began to corrode, the leaks became more serious.

That year there were two major leaks that became public. One was in Arkansas, at Damascus; the second near Rock, Kan., where two airmen lost their lives and 30 others were injured as a result of exposure to the deadly oxidizer gas.

Despite the fatalities, there was little general public concern over the Titan II.

SAC already had been forced to make major repairs in Titan operational systems. For example, the guidance mechanisms had begun to fail in the mid-1970s. A system was developed out of the Titan III space launcher and put in the Titan II.

The last firing of a Titan II missile took place in 1976 when the new guidance system was tested. It was declared a success and over the next three years, the new guidance mechanism was put into the remaining missiles.

No Titan IIs, however, have been flight tested since that date. In fact, since there are only two spare Titan II shells, the Air Force has yet to replace the Rock, Kan. missile that was destroyed by the major leak.

Since the 1978 leaks, SAC emphasis has been on developing better safety systems for handling the toxic fuel and oxidizer.

While this repair work has been going on, however, SAC has been fighting off all efforts in Congress to question the missile's safety or usefulness.

In 1979, Pryor tried to get funds for an alarm system at the missile sites to warn neighboring civilians of a leak, SAC opposed it and the senator had to be satisfied with an Air Force study on the safety of the Titan.

Meanwhile, Pryor's aide in Arkansas, James L. Rutherford III, began private talks with officers and airmen on the Titan II repair and maintenance program.

He discovered, for example, that on the day Pryor was taken to look at one Titan site in 1979, the missile at another site was leaking.

He also was told that on that day, 13 of the 18 safety devices designed to record dangerous levels of oxidizer gas in silos at the Arkansas sites were not working.

Many of the airmen assigned to the missile sites said they were worried about the constant breakdowns inside the silos.

A top technician told Rutherford that he was having trouble keeping qualified engineers working on solving the new problems that were developing on the old missile. Engineers were needed, he said, because there were no longer spare parts and repairs had to be improvised.

When the Air Force released its report on the Titan II this May, it declared the system safe for the foreseeable future and said it "would remain a highly reliable, accurate weapons system through the 1990s."

The report, however, pointed out that 19 Titan II missiles had needed one or more tank patches because of corrosion, and indication that the skin of the missile was weakening.

The only hint that perhaps something might be amiss with the weapon came in the Air Force recommendation that the refueling crews be given extra pay because of hazardous duty.

In an interview in May, Rutherford said he feared, "there is going to be a major disaster one day and innocent people are going to be hurt."