Cutting another tie to Iran, the United States is moving toward pistashio self-sufficiency, perhaps as early as 1981, government and industry sources say. $ iran used to be this country's leading pistachio supplier. But this month, as part of their escalating confrontation with the United States, the Iranians announced that they were cutting off exports here.

American growers, however, were ready for that -- ever eager -- and for reasons far removed from international politics.

Mostly as an unlikely result of the tax reform act of 1969, the San Joaquin Valley of California is blooming with pistachio trees, just now beginning to shower the red-shelled nuts on U.S. markets.

Tax tinkering in 1969 wiped out favorable tax treatment of citrus and almond groves and sent some growers scurrying for other shelters, including pistachio trees. The trees, planted in record numbers in the early 1970s, take seven to eight years to begin producing. Thus they are now maturing at a time when the United States might otherwise face pistachio starvation.

California growers this year harvested an estimated 17.2 million pounds of the nuts, up strikingly from the 1978 harvest of 2.5 million and more than half the average U.S. consumption according to U.S. Department of Agriculture economists.

"We're getting pretty close to meeting U.S. needs," said Guy Grenier, an economist with USDA's foreign agricultural service. "In two to three years, we'll have self-sufficiency in production."

Early in the year, according to Courtney Lockwood, spokeswoman for California growers, Iranians exported large quantities of pistachios here. "Since then, it's been minimal," she said. After Iranian militants took hostages on Nov. 4, U.S. longshoremen refused to unload cargo including pistachios.

"The economic war against the U.S. reached the pistachio state on Dec. 12," said Lockwood. That was the day the Tehran Times reported the export cutoff, she said. Besides Iran, Turkey is the other major exporter of pistachios.

"We have enough nuts now, and by about 1990 we should have doubled what Iran produces," said Lockwood. An estimated 31,000 acres of pistachios are expected to produce 93 to 125 million pounds, she said. Iran's current average production is about 50 million pounds.

California growers always expected to take over the U.S. market, but turmoil in Iran made their move more timely and may help open other markets, Lockwood said. "Because of the Iranian situation we've been approached by other countries. European countries, the Australians and Japan are coming to us saying they can't get anything from Iran. Because of that we're introducing the world to a better quality nut," said Lockwood.

California growers, a group dominated by five large farm companies including a Superior Oil Co. subsidiary, gave credit to merchanizaton for the quality of their pistachios.

Pistachios come in a wet hull that must be removed within 24-hours or it stains the shells black and splotchy, said Lockwood. In Iran, where most of the harvest is done by hand, the nuts are dyed to cover up the unsightly splotches. American pistachios, in contrast, are shaken swiftly from the tree by a mechanical hand that drops them into a contrivance similar in appearance to an inverted umbrella. From there, they move into a conveyor belt to be shelled within six hours and refrigerated.

Before 1969, few growers had thought much about pistachios. Only a few trees had been raised on an experimental basis, using stock from Iran, Turkey and Afghanistan. Besides the tax appeal, the boom was bolstered by Agriculture Department reports in the early 1970s that the trees were relatively resistant to disease and pests and by pistachios' potential as a profitable specialty crop.

This year, with the crop coming into its own, the growers retain a public relations firm to speak to them, and legislaton is pending in the California legislature to create a commission to assess pistachio growers for research and marketing of their crop, along the lines of citrus and avocado promotion.