Not every vacationing American is staying on this side of the Atlantic, and those who do choose to go to Europe this summer will find some attractive incentives.

There's no question that recent terrorist incidents, the Soviet nuclear accident and the weaker U.S. dollar have sharply reduced the number of Americans planning a European holiday this summer, compared to the record 6.5 million transatlantic travelers in 1985.

As a result, some tour operators -- but certainly not all of them -- are beginning to offer special bargains. A major exception is American Express, which, said a spokeswoman, does not want to be in a position of influencing someone's decision with a special promotion. "Our first concern is the safety of our clients."

At the moment, it is difficult to determine how widespread special travel incentives will be this summer. Much of the transatlantic travel industry seems to be taking a wait-and-see approach to how strong the American market will be this summer.

There is, however, an expectation in the travel industry that the transatlantic airlines will begin offering inducements, such as reduced hotel and car rental rates, to help fill flights. Air France, for example, has just announced Paris and Riviera "markdown" packages for July and August.

British Airways will offer a standby fare from Washington to London beginning June 1 that is expected to be less than the 21-day advance-purchase round trip of $669 weekdays (Monday through Thursday) and $719 weekends. With flights generally departing at less than capacity, getting a last-minute standby seat should be easier this year than in 1985.

As in the past, charter-flight operators will attempt to underprice the scheduled airlines on transatlantic routes. Martinair, a subsidiary of KLM Royal Dutch Airlines, is offering a round-trip fare between Baltimore/Washington International and Amsterdam of $399 to $483, depending on date of departure. KLM's 21-day advance-purchase fare is $819, from June 1 through the summer.

Martinair Vice President Janice Holden said the company anticipates maintaining a schedule this summer of 9 1/2 flights a week (wide-bodied planes) from 10 North American cities, down from 11 1/2 flights originally planned at the outset of the year. Martinair will depart BWI every Thursday from June 5 through Sept. 18, returning from Amsterdam on Thursday also. For information: (800) 847-6677.

One charter company, Homeric Tours of New York, specializing in travel to Greece, has introduced "supersaver" packages to Athens, a destination particularly affected by the dropoff in U.S. travelers as a result of terrorist incidents. The supersavers are priced well below the firm's customary summer programs.

So far, there is no strong indication that hotel rates in the major European cities are dropping. A chain of luxury hotels, Leading Hotels of the World, said it has no plans to lower prices at its European properties this summer. Other travel industry sources said much the same thing.

On the other hand, at least one U.S. tour operator, Trek Europa, which offers van tours in Europe for the 18-to-35 age group, said it is getting discounts on hotels now that it can pass along to its customers this summer. In the view of spokesman Mark Sheehan of Gardena, Calif., Americans going to Europe can expect to find "some seductive pricing."

In the midst of the gloomy European travel situation, there are other positive notes, remarked on by more than one representative of the European travel industry.

This year's traveling Americans won't be competing with so many of their countrymen and women for hotel rooms, restaurant seating or viewing space at the art museums. As a result, Europe will seem more European.

Also, there is less need than in recent years to book well in advance to assure yourself of an airline seat and a place to stay. Travel decisions can, if necessary, be put off for a while longer.

(Actually, this year it is more important to make reservations for U.S. destinations, not only because many Americans are staying closer to home but also because more Europeans are coming to the United States this year. The weaker dollar makes the currency exchange rate more favorable to them.)

On the negative side, many tour operators are offering fewer departures than last year, so the tour date you want may not be available. And tour options have narrowed. Trek Europa, for example, has canceled its North African excursions because of the itinerary's proximity to Libya.

Because of the rejuggling of tour schedules, it is important when you are booking a package to determine if the departure date is guaranteed -- that is, have enough people signed up to fill the customary 35-seat motorcoach so that a cancellation is unlikely?

If you do cross the Atlantic, here is a sample of the kind of bargains that are available this summer:

*Venice Simplon-Orient-Express: The standard rate for this nostalgic Victorian-era luxury train trip from London to Venice is $820 per person one-way, including all meals for the 30-hour journey. But now the return to London aboard the express is only $179 -- cheaper than the Venice-to-London air fare, according to spokeswoman Donna Samson Brunstad.

The $179 return fare is also good to other stops on the train's route: Innsbruck, Zurich and Paris.

The return trip was priced low to attract travelers reluctant to fly within Europe, said Brunstad. As a part of the package, passengers can stay at the luxury Cipriani Hotel in Venice at 40 percent off its standard rates. For information: (800) 524-2420.

*Trek Europa: This company, catering to young travelers, offers a variety of van tours throughout Europe (and North America) that include camping and picnicking along the way to cut costs. Unsold seats on these tours will be available at up to 35 percent off about two weeks before the trip's scheduled departure.

The discount obviously is aimed at the last-minute traveler, which makes it somewhat inconvenient. However, all of Trek Europa's tours leave from London, so interested participants can book a flight to England and then check with Trek Europa to see what itineraries are available at a discount.

The firm's 14-day "Alpine Lakes" tour ranges from $369 to $485 per person, depending on departure date. On the loop itinerary from London are Belgium, Germany, Switzerland and northern France.

Spokesman Mark Sheehan is optimistic about his firm's prospects this summer. The vans carry a maximum of 14 passengers, and tours depart with as few as eight or nine -- much easier to fill than a motorcoach. And younger travelers, Trek Europa's market, are more "adventurous. They're going to travel," Sheehan says. For information: Trek, P.O. Box 1338, Gardena, Calif. 90249, (800) 221-0596.

*Air France: Air France is offering two summer packages for July and August, the Paris Markdown and the Riviera Markdown, combining hotel accommodations and round-trip air fare from Washington in one price.

Depending on the category of hotel you choose, the package with lodging can be cheaper than the 21-day advance purchase air fare alone.

The Paris package goes for $749 to $1,099 per person (double occupancy) and includes air fare, six nights lodging (at the higher price, the hotel is the Crillon, one of the world's best); a half-day of sightseeing; and a chauffeured limousine for one day.

In comparison, the round-trip air fare only is $849 weekdays and $899 weekends.

The Riviera package ranges from $989 to $1,129 with a choice of hotels in Nice, Monte Carlo and Cannes. The price includes air fare, six nights lodging, continental breakfast and a rental car for six days with unlimited mileage. For information: See a travel agent or Air France sales office.

*Homeric Tours: Aware that 1986 was going to be a difficult year to attract American tourists to Greece, Homeric Tours put together several "supersaver" air, land and cruise packages at reduced rates, according to spokesman Evan Pezas.

For example, Homeric's "Grecian Delight" -- air fare from New York, three days in Athens and four days on a Greek Island cruise -- is advertised in the 1986 brochure at $1,299 per person (double occupancy) for July departures. At this price, the hotels are in the deluxe category.

For $300 less ($999), the same tour is available -- including air fare and the cruise -- except that accommodations are in tourist-class hotels. A variety of other tours is also available.

Currently, Homeric is booking its clients on scheduled airlines from New York to Athens but expects in June to operate its own charter service weekly on Thursday and Saturday using the wide-bodied planes of Tower Air. For information: (800) 223-5570.

*El Al Israel Airlines: El Al recently has begun offering land tours in addition to its flights to Israel and has put together several introductory "Sunsational" packages at reduced rates for accommodations.

For example, five nights in a Jerusalem or Tel Aviv hotel is only $39 total per person (double occupancy) for passengers booking a New York-Tel Aviv flight, which currently is $888. The packages are good through Oct. 9. For information: (800) EL AL SUN.

Certainly no travelers vacationing in Europe this summer should be lured against their best judgment by a bargain. If you are going to feel uncomfortable, then you probably won't enjoy your holiday and should not go.

But if you are going, there are bargains to be found, despite the weakened dollar.

Since special promotions can become available at any time, you should keep watch on newspaper travel ads throughout the week. Also check with a travel agent and the national tourist office of the country you plan to visit. They all have offices in New York City.

Next week's column will discuss moves by transatlantic airlines, cruise lines and tour companies to reduce or eliminate cancellation penalties on trips to Europe this summer.