Zaire announced tonight the Morocco and "another African country" will send troops to help Zaire's army fight off Katangan rebels who have seized much of the country's southernmost province.

The first contingent of Moroccan troops is to arrive Friday, government spokesman said. The second country sending troops was not officially identified but is believed to be Egypt.

At a news conference tonight, spokesmen for the official Zaire news agency also announced that China is sending 30 tons of emergency military supplies by plane, to be followed soon by a larger shipment by sea.

No information is available on the type of equipment China is sending, but observers here believe that it could include heavy artillery and tanks. Sources in the capital suggest that the plane is carrying small arms, while the ship will bring in heavy tactical weapons.

Well-informed sources said Egypt and Morocco have both pledged to send battalions of about 1,500 men each. The initial contingent of Moroccan troops will number 250, the official news agency said.

The surprise developments, which follow a diplomatic mission by Foreign Minister and Vice President Nguza Kari-Bond to several African countries, including Morocco and Egypt, is clearly an attempt to counter Angolan, Cuban and Soviet support of the month-old Katagan rebellion.

Morocco's ambassador in Washington, Abdelhadi Boutaleb, said his country had decided to assist Zaire's President Mobutu Sese Seko after he asked the Organization of African Unity for help in repelling the invasion. "Morocco simply cannot let down a brother African country going through a crisis like the one Zaire is going through," the ambassador said. "It must help Zaire to safeguard its independent and territorial integrity."

Egyptian President Anwar Sadat, who just left Washington after meeting with President Carter and other high U.S. officials, has recently expressed concern about Soviet activities in Africa and charged that Moscow is aiding the Katangans. He reportedly brought Carter letters expressing similar concern from Moroccan King Hassan and Sudanese President, President Jaafar Nimeri.

[Sudan's foreign minister, Mansour Khalid, said his country fully supports Zaire and will help it in any way short of military assistance. He said Sudan could not send troops because it was defending itself from "the same forces." Kalid, who met with Vance Wednesday, was in Omaha to visit the headquarters of the Strategic Air Command.]

Zaire's government recently increased its blasts at Angola, the Soviet Union and Cuba for providing troops, arms and leadership for the Katangans - former policemen who fled to Angola 13 years ago after the failure of a secessionist movement in Katanga (now Shaba) Province.

Zaire broke off relations with Cuba Monday, charging that proof of Cuban involvement in the Shaba "invasion" had been found on a Cuban diplomat here.

Diplomatic sources here believe that the new dimension of foreign intervention on the side of the government will have an immense impact on the military situation, possibly reversing the recent trend of easy Katangan gains.

The support of new highly trained and well-disciplined troops should provide at least part of the answer to Zaire's biggest problem: poorly organized forces with no recent experience in either conventional or guerrilla warfare.

There were also serious organizational problems as the government troops used conventional war tactics against guerrillas. The $2 million of military support equipment from the United States and the small arms provided by France and Belgium did not appear to change the situation.

A reshuffling of the top two military posts - chief of staff and regional commander of Shaba - made a noticeable difference in organization, according to two high-level diplomats who visited the area this week.

Observers here have expressed serious doubts, however, that the shift in leadership woule be enough to infuse the necessary new momentum and initiative for the government troops to hold off well-trained Katangan guerrillas.

The announcement of foreign intervention comes at a crucial moment, as the guerrillas reportedly are within a few miles of Kolwezi, Zaire's valuable mining center, which provides most of the country's foreign earnings.

There have Been several reports in the capital that Mobutu was negotiating with European mercenaries - including some who fought in the original rebellion in the early 1960s - to back up his forces.

Zaire's statement indicated that Zaire's leader first turned to African allies who "have condemned the Shaba invasion and have supported us in facing what all consider an aggression against the Organization of African Unity and national sovereignty."