A survey of diplomats and Olympic representatives from 17 Western nations here indicates that the number of tourists planning to attend this summer's Games will be less than half what was anticipated before the U.S.-led boycott campaign.

The survey suggests that the boycott will be much more painful to the Moscow organizing committee than Soviet officials have admitted. The Soviet officials have claimed that the boycott effort has failed and that it has had little impact on tourism.

At the same time, officials here have responded vaguely when asked exactly how many foreign tourists they expect this summer.

Yesterday, for example, Moscow Mayor Vladimir Promyslov said that the city now expects 100,000 foreign visitors for the Games. That would represent an enormous drop from Soviet estimates before the boycott campaign that indicated 300,000 tourists would visit the capital during the Olympics.

Later, however, Promyslov issued a clarification saying that he had been referring to the number of foreigners who would be in town at any given time during the Games.

Tourists are expected to stay here for a few days of Olympic events before leaving and being replaced by a new wave of visitors. The organizers say they expect as many as three waves during the three weeks of the summer Games, so Promyslov's clarification appeared to indicate little change.

The Soviets, however, have clearly lowered their expectations. When they now talk of 300,000 foreign "guests" in the city for the Games, they include in the total more than 25,000 athletes, journalists, officials and guests. Previously, they had stated clearly that they expected 300,000 tourists in addition to these other visitors.

Alexander Simchenko, protocol chief for the official Intourist travel agency, said that the organization expects between 260,000 and 300,000 foreigners here during the Games. He said the boycott will have little or no effect since "the number of tourists who have refused to come is very small, and in addition, we have extra applications from some countries.

Contrary to Simchenko's assessment, however, the survey indicated that at most, about 55,000 tourists from the 17 countries contracted will come to the Games. Diplomats and olympics attaches from those nations said that they had expected more than 130,000 tourists.

The survey is only an indication, since in many cases the numbers are rough estimates.

The U.S. Embassy here is now projecting that 3,000 American tourists will come to the Games instead of the 30,000 that had been anticipated. During a visit by U.S. Olympic Committee officials here in late 1978, however, USOC President Robert Kane said 50,000 Americans might come.

The 30,000 figure is based on the number of tour packages allotted by the Soviets through Russian Travel Bureau Inc., a New York firm that had a contract for 22,000 tourists through Intourist and Anniversary Tours, another firm that sources here say has been allocated 8,000 spaces for young people through the Soviet Sputnik organization.

The nations covered in the survey were: Australia, Belgium, Canada, Denmark, France, Great Britain, Greece, Iceland, Ireland, Italy, Japan, Norway, Spain, Sweden, Turkey, United States, and West Germany. j

The Anticipated tourist drop was particularly sharp among those nations whose Olympic teams will boycott the Games. The Canadians now expect about 300 tourists instead of the 8,000 previously invisioned. West Germany, which had expected 12,000 tourists, now expects no more than 6,000 and possibly fewer than 3,000, sources here said. A Japanese source said that country now expects 1,300 Olympic tourists instead of the 12,000 orginally anticipated.

There have also been large adjustments for some countries whose teams are coming against their govenment's wishes. There will be no more than 400 Australian tourists here this summer compared with 4,500 expected before the boycott campaign, sources said. A british source said that country now expects no more than 2,000 tourists instead of 7,500.

Many here expect the Soviets to pad the tourist totals to avoid embarassment. "I supect what they'll do is fill the stands with Third Worlders and the like," said one diplomat.

It will also be difficult to pin down whether the Soviets open the doors for more tourists from fraternal countries. Soviet officials have never spelled out how many foreign tourists they expect from socialist nations and how many from the West.

Simchenko said that visitors from socialist countries normally account for about 60 percent of all tourism here, but he did not say how many tourists from socialist countries had been expected for the Olympics. It was believed that the Soviets would try to attract the maximum number of tourists from capitalist countries as a source of needed convertible currency.