Stinger antiaircraft missiles from the Central Intelligence Agency's secret arsenals, intended for use against Soviet tactical aircraft in Afghanistan, reportedly have wound up in Iran where they have been turned against U.S. aircraft in the Persian Gulf.

Intelligence sources say several American-made Stingers have been sold to Iran by Afghan guerrillas with close ties to Ayatollah Ruhollah Khomeini's fanatical regime. There is reason to believe that Stinger missiles have already been used against at least one U.S. helicopter.

We have been investigating this scandal for several months; our reporting included a trip by Dale Van Atta to the Afghan-Pakistani border. Here are the pieces to the puzzle:

The Stinger scandal can be blamed largely on the CIA's obsession for secrecy and "deniability."

The Reagan administration arranged with Saudi Arabia, meanwhile, to contribute secret matching funds to pay for arms shipments to Afghan guerrillas. The arrangement is linked to the Iran-contra scandal. Former national security adviser Robert C. McFarlane negotiated with Saudi Prince Bandar bin Sultan for contributions to both the Afghan resistance and the Nicaraguan contras. Thereafter, profits from the Iran arms sales were commingled with secret funds earmarked for the Afghan mujaheddin.

The Saudis contributed $1.5 billion, sources say, to the Afghan resistance. In return for this secret support, they demanded that the CIA arms go to four favored Afghan groups. Two are hardshell fundamentalist factions -- Hezb-e-Islami, led by Gulbuddin Hekmatyar, and Ittihad-e-Islami, led by Rassoul Sayaf -- with close connections to Tehran. Both groups not only draw inspiration from Khomeini but also both want to establish an Iranian-style Islamic state in Afghanistan.

Apparently, the Saudis hoped their financial aid would placate the fundamentalists and promote tolerable relations with Iran. The likely Saudi objective was to help the fundamentalists create an Islamic state in Afghanistan, in preference to creating one in Saudi Arabia. Thus most of the CIA's arms went to two guerrilla groups that are friendly to Iran and hostile to the United States.

Of more than 900 Stingers shipped to Pakistan for distribution to the Afghan guerrillas, an estimated one-third never reached their destination. They were stolen by arms dealers, crooked CIA middlemen and corrupt officials along the way. Weapons of all description can be purchased at black-market arms bazaars along the Afghan-Pakistani border.

Informants have told the CIA that the two fundamentalist guerrilla groups have sold several Stingers to Iran. In return, Iran provides cash, indoctrination and guidance to the guerrillas. The two groups reportedly are holding back weapons for the final struggle to control Afghanistan after the Soviets pullout.

After his trip, Van Atta concluded that the CIA has simply failed to monitor, let alone protect, its arms shipments. Now, the agency has started to tighten security. CIA agents now question guerrillas closely and demand to see empty rocket cannisters before replacing Stingers.