Unable to build an instant modern army, China has begun to accelerate training and arming of its primitive but huge militia force of 60 million to 100 million men and women.

The decision to upgrade the Chinese militia, the largest force of its kind in the world, shows the seriousness with which Peking views the unfriendly Soviet forces on its northern border and the increasingly hostile Vietnamese forces on its southern border.

Although Chinese military missions are window-shopping for new weapons systems all over Europe, Peking's generals have apparently acknowledged that it will take many years to make their regular army capable of engaging the Soviets.

"The militia is really being built up," said one military analyst here. "It's a quick fix to modernization. No tanks. You just hand out a lot more rifles."

Probably no more than a fourth of the current militia forces are armed. Many still drill with ancient rifles such as pre-World War II German Mausers. But analysts say the Chinese are manufacturing and distributing more of the type-56 rifle, a Chinese adaptation of the AK47, and including the better-armed militia units in maneuvers with regular army forces.

The new national constitution, approved in March, explicity calls for strengthened control of the militia by the regular army. This lessens the chance that the militia would be used as an independent political force, as was attempted by a Shanghai faction in the Politburo that was purged after the death of Communist Party Chairman Mao Tse-tung in 1976.

But the decision to build up the militia under army control, rather than dismantle it to prevent further abuses, suggests that Peking may still see a need to use it to maintain order. Some analysts here say that without Mao to inspire people with his ideological campaigns, the government may rely more on coercive means to ensure order and productivity.

Despite the buildup of the militia, the Chinese press speaks most often of modernizing the regular army. The new training and rifles for the irregulars appear to be stop-gap measures. The leaders apparently see a place for Mao's old concept of militia-led guerrilla war, but think the Soviets will only be scared off or defeated by a full complement of modern weapons. No official Chinese commentator has so far raised the point that the Soviets might be tempted to attack an army that is quickly modernizing.

The regular army, which includes the Navy and Air Force, numbers about 3.5 million.

Compared to the awesome firepower of the Soviet forces, it is not much better equipped than the part-time militia it supervises.

Peking has sent military missions to look over sophisticated arms systems in France, West Germany, Britain, Yugoslavia, Sweden and Italy.

Yet military analysts here estimate that it would cost Peking at least $30 billion to $40 billion to buy enough equipment even to approach the Soviet forces they face. China is thought to have no more that $2 billion to $4 billion in foreign exchange available for overseas purchases and much of that is being spent to import grain.

"They may buy just 50 new model tanks from Europe, but that will be just a drop in the bucket," said one analyst. Some experts think they are more likely to buy antitank missiles, since those are cheaper than tanks as defense against a Soviet tank invasion. They could buy a few as prototypes for their own construction, but that would mean waiting for their own factories to train enough technicians and develop the proper equipment.

Even if they could quickly acquire modern weapons, the Chinese need years to train their officers in how to mix the new devices effectively in combat.

"They've got 20-year gap in the development of doctrine," said one analyst, pointing out that Peking abolished special training colleges for military officers during the Cultural Revolution of the late 1960s.

China's two top leaders, Party Chairman Hua Kuo-feng and Vice Chairman Teng Hsiao-ping, recently underlined the need for better-trained soldiers.

That training has now extended to the militia, putting a little polish on Mao's idea of a "people's war" against any Soviet invasion. The idea has been to let the Russians drive deep into Chinese territory, then unlease the militia to harass the enemy like millions of bees attacking a bear.

Many Chinese would be mowed down in such battles of men versus machines. But they would have an enormous advantage in numbers and the added boost of defending their own territory.