The United States for the first time will send a military unit to Oman to set up a temporary communications center, the Pentagon said yesterday.

Although the Pentagon's official spokesman would not disclose numbers, other sources said about 250 Army and Air Force troops will go to Oman, the Persian Gulf country that served as staging area for the ill-fated U.S. hostage rescue attempt last year and one of those the United States hopes to use for the new Rapid Deployment Force in crises.

The communications unit is expected to start flying to Oman this weekend, remain in the country the rest of the month and then leave.

Pentagon spokesman Jerry R. Curry did confirm yesterday that a communications exercise will be conducted in Oman for the first time. He said the force will consist mainly of technicians, not combat troops or military advisers.

"We are not sending combat troops there to do anything," Curry said.

The communications exercise is gearing up at the same time the Joint Chiefs of Staff are in dispute over which military command should run the Rapid Deployment Force. One idea is to set up a new Persian Gulf command in a place like Oman to send a signal to the Soviets that the United States is determined to protect its interests in the region.

Right now the RDF is under the Readiness Command and MacDill Air Force Base in Tampa, Fla. The Readiness Command, under the present setup, must approve the war plans for the Persian Gulf but would not be responsible for executing them. Critics contend this invites confusion.

In response to such criticism, the chiefs agree that the RDF should be taken out from under the Readiness Command. All the chiefs except Commandant Robert H. Barrow of the Marine Corps want the European Command headquartered in Stuttgart, Germany, to take over the RDF. Barrow, in a major split with his fellow chiefs, contends it would make more sense to put the RDF under the Pacific Command headquartered in Honolulu.

Barrow, in making his case, said it is senseless to have the European Command responsible for the land of Iran and the Pacific Command for most of the waters around it.

"It is sort of a cardinal rule," Barrow told the Senate Armed Services Committee last week, "that unless you absolutely have to, you should never have a command embracing more than one total area, particularly when they are widely separated and have different approaches to the problem."

The Pacific Command already has thousands of Marines at its disposal and the ships to transport them to trouble spots around the Persian Gulf, Barrow said. This is a "now" combination, he said, not dependent on the outcome of current negotiations for access rights to bases in places like Oman and Egypt.

In contrast to those uncertainties, Barrow said, "We do know that we have a reasonably strong naval presence today in the area" around the Persian Gulf in the form of battle groups and Marines afloat. They are under the Pacific Command of Honolulu.