The Belgian government has decided to send 250 paratroops to Zaire in a move ostensibly designed to protect the white communities of the two biggest cities of the country. News of the preparations to send the troops have leaked out here despite efforts by the Belgian government to keep the military operation secret.

The government in Brussels is understood to have consulted with the United States and Britain as well as France, with whom it sent paratroops to put down the revolt in Zaire's Shaba Province last summer.

The sending of further troops, however, is bound to be seen by some African countries as interference in African affairs and an effort by the West to boost the ailing government in Zaire of Gen. Mobutu Sese Seko.

The Foreign Ministry initially would make no formal comment on the reports that the troops are to be sent to Zaire, although some officials pointed out that an agreement covering military cooperation and the training of Zaire troops already existed.

Later, the Foreign Ministry issued a communique saying that Belgian troops would be sent to Kitona military base northwest of Kinshasa "to improve the training of Zairese units through joint exercises."

The Belgian government has been alarmed at reports of increasing disorder and violence from a number of Zaire cities, notably the capital, Kinshasa, and Bukavu, the capital of Kivu, the eastern region. It is understood the troops will be available to protect the 30,000 whites, mostly Belgians, in the Kinshasa area and also, if needed in Kivu.

The moves to send the troops is bound to excite considerable controversy in Belgium, too. There was criticism last summer at the delay before Belgium agreed to send troops to put down the invading rebels in Shaba, but some members of the Socialist Party, to which Foreign Minister Henri Simonet belongs, fear that sending troops will itself put the white population in greater danger.

The growth of urban discontent and violence has followed on the near collapse of the Zaire economy in recent years. Inflation is reportedly running at more than 100 percent a year, unemployment in the cities has soared and there are severe food shortages.

In an effort to bolster the economy and to find a way to prevent Zaire's massive debts to Western banks bringing about total collapse, a group of major Western countries are studying economic and proposals.

The International Monetary Fund has sent representatives to oversee the operations of the Zaire central bank and the Ministry of Finance, and the Mobutu government has promised sweeping economic and political reforms and curbs on corruption.

Details of the plan to send the paratroops were released to Belgian journalists today in a private briefing given by Simonent. The foreign minister, who said that the decision was so far known only to himself and the acting prime minister, Paul Vanden Boeynants, asked the Belgian journalists not to write about the operation.

Despite the large number of Belgians and other Europeans still working in Zaire, there has been a growing movement among members of the Zaire community in exile to persuade European governments not to appear to be giving support to Mobutu.

At one time last year the Belgian government, under pressure from the Mobutu government, tried to muzzle leaders of Zaire anti-Mobutu political groups operating in Brussels.

Simonet is expected to argue that, in sending the troops, Belgium is not supporting Mobutu but honoring a military agreement and taking precautionary steps to prevent the repetition of the events in Shaba when about 200 whites -- as well as hundreds more black -- lost their lives, although most white casualties were only after news of the troops landing was known.

The Mobutu government forces are still being supported in Shaba by Moroccan troops which are reportedly being partly financed by both France and Belgium.