In a move sure to anger some members of Congress, the Carter administration has approved for the first time the sale of x-ray inspection devices and metal detectors to the Soviet Union.

The export of the metal detectors was said by the Commerce Department to be for use at Soviet airports and at the 1980 Olympic Games in Moscow to search out weapons carried by possible hijackers or terriorists. The X-ray inspection devices are to be used during the Games along with the metal detectors to search the belongings of athletes and spectators attending the Olympics.

"We had no compunctions about approving the export of this equipment," said one Commerce official who asked not to be identified. "These particular devices are considered to be protective of human rights, not harmful to them."

That has not been the view taken by many members of Congress. The chairman of the Senate permanent subcommittee on investigations, Henry M. Jackson (D-Wash.), put strict controls four years ago on the export to the Soviet Union of metal detectors and X-ray inspectors.

In 1974, the Soviet Union tried and failed to get export licenses for a range of devices classified as crime-and riot control equipment. These included voice identification machines, X-ray inspection devices and metal detectors.

"It's ironic, said Richard Perle, an aide to Sen. Jackson, "that the Nixon administration should have added things to the export control list that the Carter administration is now prepared to sell."

Congressional critics such as Jackson and Rep. Clarence E. Miller (R-Ohio) fear that the technology might be used to police political dissent.

"It's a moral issue," Perle said."How do we know how these devices will be used when the Olympics are over? The United States should not be doing business with the KGR."

Two separate export licenses involving the sale of metal detection equipment and X-ray inspection devices were approved by the Commerce Department in the last few months.

The first license was granted July 6 and involved the sale of crime detection equipment worth $70,295. The equipment was identified as "metal detectors" for use in Soviet airports.

The U.S. manufacturer was not identified.

The second license was approved Oct. 13 and involved the sale of police equipment worth $1,277,370. This equipment was said to be "metal detectors and X-ray inspection devices" for use during the Olympics. Again, the manufacturer was not named.

Commerce Department sources said most of the metal detectors would be used to search people going in and out of the dormitories housing the 12,000 Olympic athletes. One Commerce source said: "Everybody remembers the massacre of the Israeli athletes during the 1972 games in Munich. Nobody wants that repeated."

Soviet experts in the State Department say that Soviet authorities are "scared to death" that political dissidents might attempt to focus world opinion on their cause by demonstrations during the Games. The Soviets privately have told some American diplomats, that they will not allow demonstrations during the Olympics.

The Soviets also estimate that the Olympics will bring 200,000 foreigners to Moscow and they are concerned sympathizers to the dissident cause might be among them. Said one State Department source: "They even worry that hippies and yippies might come for the Olympics, carrying God knows what kinds of drugs in with them."

No matter what use the Soviets make of metal detectors and X-ray inspectors during the Olympics, critics are concerned that the technology will wind up in the hands of the KGB [the Soviet secret police] to be used for suppression of dissidents.

"Obviously, they [the Soviets] can get these things elsewhere - but that's not the point," Perle said. "This is another example of policy that should be based on moral grounds and instead is based on business-as-usual grounds."