The U.S. government is fronting an arms deal in which Israel, without being publicly identified as the source, is selling Indonesia used warplanes obtained from the United States.

Pentagon officials confirmed yesterday that Israel is shipping Indonesia 16 A4 fighter-bombers for $25.8 million in the first such third-country sale of U.S. warplanes.

The Pentagon issued a press release on June 14 about the A4 sale to Indonesia but did not disclose that Israel -- and not the United States -- is the seller.

One defense official said that neither Israel nor Indonesia wanted the U.S. government to disclose the source of the planes. He said, however, that Congress was told confidentially that Israel was the seller.

A government source cautioned last night that with word leaking out that Israel, not the United States, is the source of Indonesia's planes, the deal may fall through even though all three governments had agreed on it. The United States, the official said, may find a way to sell the planes itself rather than serve as Israel's broker.

"This sale," the Pentagon said in its press release on the A4 deal, "will contribute to the foreign policy objectives of the United States by helping to improve the security of a friendly country in Southeast Asia."

Israel has bought 355 A4 Skyhawk, single-seat fighter-bombers and 210 F4 Phantom fighter-bombers from the United States over the years.

The Indonesia sale, made with Carter administration approval, could turn out to be the first of several, with Israel disposing of its old American warplanes as its air force obtains the newer U.S. F15 and F16 fighters.

Under existing agreements, a country such as Israel that buys weapons from the United States must obtain U.S. permission before selling those weapons to another, or third, country. It therefore will be up to the administration to decide how many U.S. planes Israel can sell to other countries.

President Carter has warned against "proliferation" of aging superpower weapons as they become in surplus and Third World countries seek to buy them.

When queried yesterday, the Pentagon could not cite a previous instance when warplanes such as the A4 Skyhawk jet had been sold by one foreign buyer to a third country. But they did not rule out the possibility.

Paul Warnke, former director of the U.S. Arms Control and Disarmament Agency, once said that "anybody who thinks" existing controls over sales of U.S. weapons to third countries are adequate "is smoking opium."

Some aerospace executives are reacting angrily to the spreading news that Israel is the actual source of the A4s going to Indonesia.

They complain that Israel, because Congress usually forgives a large portion of the loans to it, is getting U.S. planes at a discount and then selling them at world market prices.

American firms are vying for that same kind of business. Some of them specialize in reconditioning used planes and selling spare parts to keep them running.