The Carter administration is studying plan to ask India, Israel and South Africa to allow periodic inspection of their secret nuclear plants.

The plan would involve a promise by the administration not to ask the three how much plutonium and weapons-grade uranium the secret plan's have produced as long as the countries open up the plants to future inspections by the International Atomic Energy Agency in Veinna administration sources say.

This "don't-look-back" aspect to President Carter's policy against nuclear weapons spread now is being discussed in the White House and the State Department as possibly the only way to get India, Israel and South Africa anywhere close to the camp of nations signing and ratifying a treaty that prohibits the spread of nuclear weapons.

None of the three has signed the Non-Proliferation Treaty and none has allowed any inspection of the secret nuclear facilities each has in somewhat inaccessible regions.

India built a research reactor and a plutonium extraction plant outside Trombay for $30 million. The plutonium plant has been extracting the metal from spent nuclear fuel since 1964. It was this plutonium that India used to make and explode its first atomic bomb in 1974.

Israel has a research reactor and a plutonium extraction plant outside Trombay for $30 million. The plutonium plant has been extracting the metal from spent nuclear fuel since 1964. It was this plutonium that India used to make and explode its first atomic bomb in 1974.

Israel has a research reactor that produces about 15 pounds of plutonium every year at Dimona in the Negev Desert. Experts believe a plutonium extraction plant is connected to the reactor at Dinona, which has been in operation for 20 years. Israel twice turned down the requests of 11 U.S. senators late last year to visit the Dimona plant.

Of the three facilities the White House would like to see safeguarded the South African uranium enrichment plant at Pelindaba is the newest.

Never opened to U.S. eyes, the plant is believed to have gone into production more than a year ago when it began taking new uranium and enriching it with the isotope U-235 to make uraniun for electricity.

Unlike the plants in India and israel, the Pelindaba facility does not produce plutonium, which can be made directly into weapons. But the Pelindaba plant could conceivably produce weapons-grade uranium. The difference between uranium for power and for weapons is that weapons material contains about 15 times more 1-235 than power-grade uranium.

Administration sources stressed that their strategy "not to look back" at what the plants have produced is still in the formative stage. None of the three countries has been approached with the plan to see how it would react.

The three plants involved are considered the toughest nuclear facilities in the world to bring under safeguards. No American has seen what the Indian and Israeli plants have been producing for 10 years and no American has ever been to Pelindaba to observe how it works.