Foreign diplomats and foreign governments will have to get permission from the State Department any time they want to buy, sell or rent houses or other property in the United States, under a new federal law.

The new authority is intended to give the United States leverage for demanding better treatment of our diplomats overseas, because it will be applied on a reciprocal basis, said authorities in the State Department and on Capitol Hill.

Thus, with friendly countries, the permission is expected to be largely a pro forma requirement, while it could be used strictly in dealing with countries making life uncomfortable for our diplomats.

"If a country gives us a problem, we give them a problem. It's tit for tat," explained Robert K. Boyer, staff consultant for the House Foreign Affairs Committee. "In practice, you would find it applying mainly to communist countries, because they give us more problems."

The Foreign Missions Act, signed into law in August and effective in October, provides that the State Department may require that every real estate acquisition of a foreign government be subject to prior approval by the newly created Office of Foreign Missions.

The specific requirements have not been formalized yet, said James Wood of the foreign missions office, but it is known that the department has drawn up a form, in which all concerned U.S. and city agencies, including the Park Police and Metropolitan Police, would be informed of and sign off on each application.

Boyer noted that, if it is applied strictly, the law would allow the State Department to tell diplomats from some countries where they have to live and how much they have to pay. Actual practice, however, is unlikely to be that severe because the idea is to use the law as "a rapier rather than a baseball bat" in getting better living conditions for our own diplomats, Boyer added.

The law also enables the State Department to place conditions or restrictions on utilities, supplies, transportation, services, travel and protective services used by foreign missions.

The act could also apply to international organizations such as the European Economic Community, the World Bank, the Palestine Liberation Organization or United Nations diplomats.

Before the Foreign Missions Act, the United States had no means of retaliating against the diplomats of foreign countries that put stringent restrictions on our overseas representatives, particularly communist countries.

While the United States prefers to buy rather than rent overseas, in some communist systems this is not allowed. The new act would enable the U.S. government, in turn, to prohibit these countries from owning any property in the United States, according to State Department and Hill sources. But, Boyer added the act probably will not be used in that way.

Boyer, who recently returned from a trip to China, gave the city of Guang Zhow (formerly Canton) as an example. "They've got all the U.S. diplomats stuffed into a hotel there," with no laundry or cooking facilities, even though it is a large consulate. Meanwhile, Chinese diplomats have been able to get their pick of decent housing here, he said.

"This is a good test for the Foreign Missions Act," Boyer said.

With the new law, for example, the U.S. government would be able to tell the Chinese that unless they provide decent housing in Guang Zhow, their rents in Chicago would double immediately, with the increase becoming, in essence, a fee that the State Department would collect, he said.

The State Department is working on regulations to implement the new act, and these should be out soon, said Wood.

The law allows the department to require that a mission notify the foreign missions office any time it wants to acquire, sell or change the use of real property, giving the office 60 days to disapprove the action. It also specifically allows for a fee or surcharge to be paid to the office.

Wood said the missions office hopes to notify real estate brokers and groups of the new requirements that might be imposed on foreign missions in buying or selling property, but that neither real estate agents nor home sellers will be held responsible for making sure the missions adhere to the rules.

"We have pretty much protected the vendors in this," he said.

The new law also allows chanceries, or embassy office buildings, to be located anywhere in the District of Columbia that is zoned for commercial, industrial, waterfront or mixed use. It also permits chanceries to be located in medium-high or high density residential areas or in any area that includes office uses, although each case would be subject to disapproval by the District's Board of Zoning Adjustment.

Wood claimed that before the act, the District's policy toward chanceries was discriminatory, particularly against those of Third World countries.

City officials had objected strenuously to early drafts of the Foreign Missions Act, which they said would strip the city of authority to restrict the location of chanceries. Under the final version, the city zoning authorities will continue to review most applications for chancery moves.