China recently staged its largest known peacetime military maneuvers, combining at least 100,000 troops from the Army, Navy and Air Force for massive exercises in a mountainous region northwest of Peking, according to Western military sources here.

Peking television tonight broadcast a 10-minute film of the maneuvers, showing a full panoply of Chinese armor, aircraft and artillery. Tanks were shown rolling over rocky terrain while Mig19s flew overhead, paratroopers dropped out of aircraft and rocket launchers fired.

Practically the entire Chinese civilian and military leadership was on hand to review the extraordinary exercises. The group was headed by Deng Xiaoping, the first time he has been shown wearing an Army uniform since he took over as chairman of the military commission three months ago.

No official explanation was given for the maneuvers, which Western military sources said were conducted about 100 miles northwest of Peking along what is thought to be the most likely invasion route if Soviet troops stationed on the nearby Mongolian border ever invaded.

Even though the Sino-Mongolian border has been quiet in recent years, foreign military analysts said, the maneuvers, believed to have ended Sept. 10, could have been designed to show the Soviets that they would meet substantial resistance if they decided to attack China.

Foreign analysts also believe that the maneuvers may be part of Peking's campaign to raise the prestige of the military, which has suffered a series of recent setbacks, including sizable budget cuts, loss of perquisites for officers and criticism of the founder of the People's Liberation Army, the late party chairman Mao Tse-tung.

Military regions are known to stage annual maneuvers, but not on the scale of the recent exercises, said these analysts. Those maneuvers were the first to draw so many men from the three military branches and the first to display so many kinds of warfare, said the foreign experts.

No official count of the troops staging the maneuvers was given, although Peking television said that Deng reviewed 53 military columns after the exercises. Foreign analysts with access to the Chinese military estimate that at least 100,000 troops took part, which would make this the largest known peacetime maneuvers in more than 30 years.

As another explanation, one Western observer said that the Chinese military has been working hard to correct communications and coordination problems that became apparent during the 1979 Sino-Vietnam conflict. China's war effort was complicated by such mistakes as failure to get food to the front.

The exercises northwest of here, which brought together so many different kinds of military units and disciplines, may have been the culmination of special training "to show that they can get along with each other and put it all together when they want to," said this analyst.

Zhangjiakou, the area where the maneuvers were held, is a hilly, rugged region with many of the communications and transportation problems that had handicapped the Chinese troops who entered Vietnam through similar terrain along China's south and southwest borders.