WASHINGTON (AP) _ The Reagan administration gave final approval to sell $900,000 worth of equipment containing U.S.-made computers to Iran, despite objections by Defense Secretary Caspar Weinberger, administration and industry officials said today.

The officials, who spoke only on the condition of anonymity, said the National Security Council, asked to mediate the dispute, gave the go-ahead for the sale last week.

Weinberger had objected to the sale, claiming the United States should not be providing any aid to the Iranian regime. However, Commerce Secretary Malcolm Baldrige and Secretary of State George Shultz approved of the proposed sale, saying the computers involved had no military application.

Some $70 million in U.S.-made computers have been shipped to Iran over the past two years.

However, the transaction represents the first major export to that country since the disclosure in later 1986 that the administration had secretly approved the sale of U.S. weapons to Iran as part of an effort to gain the release of Americans held hostage in Beirut.

The computers in the proposed sale are the the relatively unsophisticated PDP-11 made by Digital Equipment Corp. of Maynard, Mass. Digital itself did not apply for the license. It was applied for by a Swiss company, Brown, Boveri & Co., which has incorporated the computers in a system it plans to sell to Iran for monitoring electric power generation.

A spokesman for Digital, Jeffrey Gibson, confirmed that the application had been approved by the government and that the equipment in question can now be shipped by Brown-Boveri to Iran.

A second application involving Digital equipment that was part of the dispute, a $30,000 add-on-memory device proposed for sale to Iran's news agency, has not been approved and apparently is still before the NSC, Gipson said.

Last month, Baldrige told a Senate Banking subcommittee he was baffled by Weinberger's opposition to the sale.

''These computers have technologies that are eight to 10 years old,'' Baldrige said at the time. ''I see no reason to put U.S. manufacturers at a disadvantage.''

He argued that under existing rules controlling exports, the same computers could be sold directly to the Soviet Union without posing a threat to national security.

Since 1984, the United States has not permitted the export to Iran of goods that could have military applications.