Foreign tourists will visit the U,S, in growing numbers during 1978, the United States Travel will be the predicts, buy nobody knows whether this will be the result of lower air fares, improved economic conditions abroad or other factors.

Because of the explosion of air fares for both overseas and domestic travel on scheduled carriers and the continuing changes in the charter markets, travelers are confused about what to do, a USTS spokesman said.

But while some hoteliers and restaurants are worked both about proposed U.S. tax law changfes that would crub deductions for business launcheous and regulations that already have curtailed some convention business abroad, one executive see "a bumper year" ahead for hotels in this country.

A recent survey indicates that the American motorist is not ready to forego vacations by automobile, regardless of lower air fares and even is gasoline prices continue to increase.

Industry spokesmen acknowledge that all predictions hinge on world economic conditions and the price of oil.

The U.S. Travel Service, which is part of the Commerce Department estimate that about 20 million foreign visitors will arrive in the United States in 1978, and 8.1 per cent increase over the 18.6 million forecast for 1977. The three countries sending the largest number of visitors here are Canada, Maxico and Japan, in that order. European visitors account for about a fourth of the traffic.

The European Travel Commission, which embraces 23 national tourist organization, estimates that 2 million Europeans will travel to this country this year, a 3 per cent increase over 1977.

But though the commission predicts confidently that 1978 "will be biggest year in history for AMerican travel agent Andy Spielman said he believes the ETC privately is concerned about the impact of new air fares and U.S. tax regulations.

Spielman, vice president of Waters Travel, said that many European hotels are reporting record booking on foreign exchanges has caused concern in travel circles. A number of wholesalers of package tours, working with a narrow profit margin, have already raised their prices to compensate, and if the decline should continue there is always the possibility that some U.S. comsumers mat decide to cancel or curtail their overseas travel plans this year.

On the other hand, foreigners whose strong currency merits a favorable exchange rate would have more dollars to budget for a U.S. vacation.

Spielman agreed with a USTS complaint that many travel agents have been more knowlegeable about planning a trip overseas than a U.S. itinerary, which has had a negatives effect on foreigners seeking to vacation here.

"But the situation is better than it was before," said Spielman, who is a long-time official of the American Society of Travel agents and a worlf traveler. He noted that "European travelers are less demandind. Perharps one in 10,000 American will be content to take a room without private bath."

A serious deterrent to demestic tourism, according to Spielman, is "the provincialism of state travel directors who are loyal to theri home constituencies and want to keep visitors there for two weeks. The same thing if true in Europe.

"This is not what tourists want after traveling a long distance - they like to spend a few days in each place, not stay in one state."

The air fare battle, begun with the initiation of low-cost, charter tour packages, was intensified when Britain's Laker Airway turned the already unsettled international fare game turned into a free-for-all. Offering no frills, no reservation on his New York-to-London-Skytrain, Laker had 2,415 seats a week in each direction. A round trip costs $236. (Early figures show Skytrain is carrying a slightly higher percentage of passengers on the westbound London-New York run.)

Pan Am, TWA and Britis Airway each are now offering 1,050 budget/standby seats a week in each direction between New York and London. The round-trip price is $256 (for either fare, though restrictions and requirements differ).

"We're very encourage by the fact that it's a new market and that it makes transatlantic travel available to people who haven't traveled before and who possible would not have traveled if the fares hadn't been reduced," a British Airways spokesman said.

Pan Am reported that the budget fare is carrying "something like 5 per cent" of the airline's traffic in that market, and said traffic is running extremely strong. The budget concept is being expanded to the Pacific, althought some foreign governments have refused to approve the fares.

Another major international fare, and one not limited to the New York-London route, is the Super Apex (now $323 round trip from Washington to London).

There are also Alitali's international rate-busting fares to Italy, now matches by other airlines, not to mention bargain U.S. domestic fares such as the "Super Saver," "Super Coach," Eastern's "Townsome," Allegheny's "Liberty" and the New York-Miami-/Fort Lauderdale "Super No Frills."

"Remember that Europeans are interested in finding sun when they come here, especially winter," said a TWA spoeksman, pointing to the new low Miami fare.

Meanwhile, the supplemental (charter) airline - which took 14 per cent of the protesting actions by the Civil Aeronautics Board and the Carter administration that permitted the scheduled carriers to reduce their fares. Supplementals and charter packagers charges that these low "competitive" fares will enable the major airlines to undercut the charter market, put them out of business, and then raise fares again, Scheduled airlines also fly charters.

In 1976 about 22.9 million Americans traveled to foreign countries, according to the USTS. They spent $9.5 billion. International tourism receipts that year totaled $40 billion. Nearly $7 billion of that total was spent in the United States. The resulting "travel gap" of about $2.5 billion was 14 per cent lower than in 1975, acording to USTS.It is shrinking, but it still figures in the deficit.

Patrick Foley, prsident of Hyatt Hotels, said that the chain's advance bookings indicate that 1978 will be a bumper year in the industry.

HIs evaluation received some support from the annual U.S. lodging industry study recently complete by Laventhol and Horwatch, an internationl accounting firm specilizing in leisure time industries which predicted a slightly occupancy rate than in 1977. However, the firm said that, due to increased operating costs, profits will be as encourage ing as sales.

And a "national probability samplying" by the 3M National Advertising Corp indictated that "of all households taking vacations in the United States, 80 per cent utilize their auto on one or more" of those trips. If gas prices reached 80 cent a gallon, "about eight out of 10 those households would not change their plans. The survey also showed that the number of travelers who go by plane, train of bus and then rent a car is increasing.