American military experts are accompanying the urgent shipments of sophisticated tanks, antiaircraft weapons and jet fighters that the Carter administration is sending North Yemen in an effort to stem a continuing invasion from South Yemen, administration officials disclosed yesterday.

The small Mobile Training Teams that are being dispatched to the mountainous, remote Arabian Peninsula country for tours of several months each involve a total of about 70 U. S. Army and Air Force instructors, Pentagon sources said. A twoman Army team is in North Yemen's capital now.

The decision by the administration to accelerate the pace of the previously scheduled visits by U.S. military teams into Sanaa became known as the three-week-old border war between the two Yemens appeared to escalate. The State Department confirmed that South Yemeni Mig fighters had bombed inside North Yemen.

The raids were described by North Yemen radio as having occurred in the Harib area almost 100 miles southeast of Sanaa. State Department spokesman Thomas Reston said the administration had no details of the attacks and could not identify the nationality of the pilots.

In a related development, the administration has decided to send a U.S. general to Saudi Arabia to coordinate the emergency shipments of Saudi and U.S. weapons to North Yemen, according to U.S. officials.

After an urgent meeting on the Feb. 23 invasion of North Yemen by tankled forces from the south, President Carter decided last week to demonstrate U.S. resolve by extending full and immediate support to North Yemen, which is allied to its northern neighbor, Saudi Arabia. Carter has put special emphasis on U.S.-Saudi ties since coming to office.

South Yemen is ruled by a militant Marxist government and is host to 1,000 Soviet advisers and an undetermined number of Cuban and East German military experts. U.S. officials said yesterday that intelligence reports indicate that Ethiopian soldiers have also recently arrived in South Yemen, but their role is not clear.

U.S. officials insisted that the military instructors would not be involved in combat operations and would be kept in Sanaa, away from combat zones. American logistics experts will also be accompanying the $400 million arms package to North Yemen but they will leave the country as soon as they have finished delivering the M60 tanks, long-range artillery and other weapons, according to these officials.

At least two U.S. Mobile Training Teams have visited North Yemen in recent months as deliveries began on the first $100 million worth of military equipment, which is being paid for by Saudi Arabia. President Carter's decisions last week opened the way for greatly accelerated deliveries of a second Saudi-financed package that includes a squadron of F5E fighters.

U.S. officials said there was no serious division of opinion within the administration about speeding up the training team schedules since the small numbers involved should not affect the military balance between the two Yemens nor touch of off an escalation of Soviet help. But there reportedly was official discussion about the dangers that terrorist attacks on U.S. instructors could draw the United States more deeply into the conflict.

The first sign of controversy over the quick, high-profile response by the administration to the Yemen war came yesterday in a biting attack on the Yemen policy delivered in the House by Rep. Les Aspin (D-Wis.).

"The administration is about to change its foreign policy from relatively passive to intensely active, yet in a highly arbitrary fashion," Aspin said.

"The president now feels that it's time we looked concerned and tough, and he is simply picking the first bet to come along. Yemen may be a particularly bad bet on which to wager our prestige" in a conflict that is more tribal than ideological, Aspin said.

He voiced particular concern that the administration is airlifting heavy equipment that North Yemeni troops are not trained to use, meaning that Saudi or other foreign Arab forces will have to be brought in to operate the tanks and aircraft if they are to be used against the invasion.

In a telephone interview after the speech, the Wisconsin Democrat said he had been told by Pentagon sources that the National Security Council had asked the Pentagon last week to draw up an options paper that specifically included contingencies for introducing U.S. ground forces into the conflict or, as an alternative, to send U.S. Marines to guard air bases while the deliveries were being made.

Asked about the charge, David L. Aaron, deputy presidential assistant for national security, denied that the council had requested such plans from the Pentagon. "It just isn't so," Aaron said, adding that administration policy would not allow combat troops be sent to North Yemen.

Citing conversations that he said he had had with "officials several layers down in the bureaucracy," Aspin said in the speech that State Department officials "are saying that the atmosphere is reminiscent of Vietnam in 1963."