Defense Department officials, in an evident effort to allay concern over deepening military involvement in the Arabian peninsula, said yesterday that the number of U.S. experts being sent to North Yemen would be less than 100 and that none of them would have a combat mission in that nation's border war.

Spokesman Thomas Ross said that the role of "less than 70" uniformed Mobile Training Teams would be "training in rear areas."

Another group of 25 experts, mostly civilian technicians, would be assigned to North Yemen with the squadron of U.S. F5 interceptor planes that is part of the U.S. military plan to support the pro-western North Yemen in its war with pro-Soviet South Yemen.

Ross also revealed that an undetermined number of North Yemen pilots already have been receiving F5 training in Saudi Arabia since January and could be ready to handle this aircraft in a matter of weeks.

The 12 Northrop-built F5s will be shipped from California to Dahran, Saudi Arabia, around March 15.

Pentagon officials pointed out yesterday that some North Yemen pilots are proficient with Sovietbuilt Mig17 aircraft and should be able to make the shift to the American interceptors without a long training period.

It was unclear whether the new shipment of F5s, costing $300 million and paid for by Saudi Arabia, would remain in Dahran or would be shifted later to North Yemen.

Ross said that "as many as 100 to 200 persons could be involved in F5 support," but that all but about 25 would remain in Saudi Arabia. Most were described as "contractor personnel" from Northrop, with the job of assembling, providing technical assistance and supervising aircraft maintenance.

It was left unclear whether American pilots would fly the planes once they reached their initial base in Saudi Arabia. However, Ross stressed that "there is no intention for them to fly the planes in or over Yemen."

Since U.S.military aid to Cambodia and South Victnam

Since U.S. military aid to Cambodia and South Vietnam escalated into a massive U.S. military involvement in the 1960s, technical military assistance has been a sensitive issue. Defense Department officials say however, that, thus far at least, most congressional reaction to the U.S. buildup in the Arabian peninsula has been supportive.

Pentagon officials stressed that, in regard to the mobile training teams, it was normal for such teams to accompany military hardware to many different countries.

"These are not Burt Lancaster types out with the troops in the bushes... these are specialists in that type of equipment," said one official.

Two U.S. experts already have arrived in Yemen to assist in training Yuemeni soldiers in the use of the Vulcan antiaircraft gun.

In addition to the Vulcans and the F5s, the Carter administration has ordered the immediate shipment of tanks, personnel carriers and other equipment to North Yemen.

Reports on the border fighting were conflicting, and the Pentagon had no new information on action taking place in the 9,000-foot-high mountain passes.

Syrian Foreign Minister Abdel-Halim Khaddam said that the two Yemens have begun implementing Arab Council resolutions aimed at ending the clashes, according to a Reuter report from the North Yemen capital of Sana. But there were other reports of North Yemen air raids against South Yemen.