The dramatic decline in the dollar in the past year doesn't seem to have stopped Americans from planning a vacation in Europe this summer and fall. All indications suggest transatlantic travel is on the rebound, and some tour organizers already see 1987 as a "boom" year.

There's no question that Europe is costlier this year. In Austria, Germany, Switzerland, France, the Netherlands and Belgium, where the dollar has weakened the most, the dollar buys from 15 to 20 percent less than it did 12 months ago. As a result, this probably is not the year for shoppers wanting to bring home suitcases loaded with bargain purchases.

But travelers interested in Europe's arts and its ambiance can still enjoy these pleasures on a reasonably affordable budget -- if they don't demand luxury hotels and Michelin-starred restaurants. In some aspects, Europe remains much cheaper than the United States. For example, the Royal Danish Ballet in Copenhagen is supported by national subsidies, and a ticket for the best seats is only about $10.

In 1986, fear of terrorism in Europe kept many Americans at home, and the European travel industry worried that a weak dollar -- substantially raising the price of a week or two on the Continent -- might have almost as detrimental an effect on their business. That hasn't proved to be the case. (At the moment, the dollar seems to have stabilized, but this could change at any time.)

About 5.5 million Americans are expected to visit Europe this year, an increase of 10 percent over 1986, according to estimates of the European Travel Commission, which represents 23 West European nations. Great Britain and the Scandinavian countries seem to be the most popular destinations. But Italy and Greece, among the hardest hit in last summer's tourist dropoff, also are drawing large numbers of Americans again.

Travel Weekly, a trade publication, polled 200 travel agents recently, and more than 80 percent of them reported increased bookings to Europe this year. Pamela Hanlon, a spokeswoman for Pan Am, a major transatlantic airline, says, "Our traffic really is better than we anticipated." Saga Holidays of Boston, a tour company that caters to the age 60 and over traveler, says it is enjoying "an extraordinary busy summer travel season." The Belgian Tourist Office in New York says requests for travel information for the six months ending in June increased 50 percent over the same period last year.

The main reasons for the resurgence, say these and other tour organizers, is the absence of headline terrorist incidents in the past year and the fact that Europe traditionally appeals to many American vacationers. Those who postponed a trip last summer are eager to go this year.

"The public really wants to go to Italy," says Mario Perillo of Perillo Tours of New York, which specializes in organized trips to that nation.

In terms of tour packages sold, says Perillo, "1985 was a superb year" -- that's when a strong dollar made Europe a bargain -- and "1986 proved to be one of the worst." So far, 1987 is not up to 1985 levels, but it's "pretty damned good." He's optimistic that in 1988, Italy will again see as many American tourists as it did in 1985, when a record 6.5 million Americans crossed the Atlantic.

The dollar's decline has had a definite impact on the price of a European trip. Travelers pursuing European tour brochures may find, when they go to book, that some tour operators will add a surcharge to the printed prices. This is because the brochures were printed months ago before the dollar's steep drop. Food and lodging arrangements now cost the tour organizer more, and those costs are in many cases being passed on to the customer.

But other tour companies, including Perillo, are guaranteeing their rates. "We have every moral and legal right to say to the public, 'We need an extra $100.' However, since the convalescent {Italy} is getting better -- it was very sick -- we're swallowing the difference. I feel that we're subsidizing the patient."

Greece, another traditional destination that was shaken badly by terrorism fears, is in a unique position this year and quite understandably is capitalizing on it. The dollar has not lost value against the Greek drachma in the past year; indeed, it may even have gained a fraction. As a result, "Greece is Europe's best value," says Peter Koujoumis of the Greek National Tourist Organization.

The prices for Mediterranean cruises departing from Athens are down by 5 to 20 percent, he says, and overall Greece is anticipating a 30 percent increase in tourism this year compared to last. "We are very optimistic."

Travelers probably will want to keep a closer watch on their spending habits this summer because of the dollar's decline. This may mean shying away from some luxury-class hotels, where reports of a $5 glass of orange juice or $14 per person for a continental breakfast (coffee, sweet rolls and juice) are not uncommon. However, you won't have to search far to find breakfast at more reasonable prices.

Keeping in mind the traveler on a more modest budget who is looking for a comfortable room and good food, the European Travel Commission recently surveyed its member nations and came up with country-by-country figures for what an independent traveler (not on an escorted tour) might expect to pay for lodging and meals from now through the fall.

Here is a sampling of the prices reported in that survey. They will, of course, fluctuate as the dollar rises or falls between now and the time you travel:

Great Britain: Visitors to London, which generally is more expensive than the rest of the British Isles, can obtain a free booklet, "London Value Hotels," listing hotels in two categories -- those below $45 a night (for two people) and those between $45 and $68. For a copy, contact the British Tourist Authority, 40 West 57th St., New York, N.Y. 10019, (212) 581-4700. In the countryside, economy hotels average $23 to $35 (for two people), and the rate for medium-priced hotels is currently $37 to $53. Farmhouse accommodations can be found beginning at about $16 per person a day, which includes the evening meal.

Dinner in a moderately priced restaurant may cost about $12 per person or even cheaper if you eat in a pub. The British Tourist Authority can provide a "London Restaurant Guide."

Ireland: A room for two in an economy hotel is about $30; in a medium-priced hotel, it's about $55. Bed-and-breakfast inns are about $15 per person a day, including a hearty breakfast. Dinner in a moderately priced restaurant should be about $11 per person. Any restaurant that displays the symbol of a smiling chef serves a low-priced tourist menu. A booklet listing such restaurants, "Dining in Ireland," is available from the Irish Tourist Board, 757 Third Ave., New York, N.Y. 10017, (212) 418-0800.

France: Throughout the country, hotels average about $50 to $90 a night (for two people) although they are somewhat higher in Paris. Other lodging possibilities include pensions at about $45 a night and farmhouses, $40. Low-cost national hotel chains are the Ibis and Climat de France.

Fixed-price menus are standard in France, and they average about $15 to $20 per person for dinner, which also covers tip and tax. A dinner in a moderately priced restaurant should be about $25 to $30 per person.

A booklet, "Paris on a Budget," lists reasonably priced hotels and restaurants in the capital. For a copy, write "Paris on a Budget," French Government Tourist Office, P.O. Box 2658, Lake Ronkonkoma, N.Y. 11779.

Italy: Once one of Europe's best bargains, Italy now can be fairly expensive. First-class hotels average between $100 and $200 a night (for two people). But pensions can be found almost anywhere, and many can be very charming. They range from $40 to $66 a night. An Italian tourist menu is about $15 to $17 per person for dinner.

Austria: A room in a moderately priced hotel in Vienna ranges from $50 to $80 (for two people). Outside the capital in Graz, Innsbruck and Salzburg, it's a bit cheaper at $40 to $80. Dinner should cost between $12 and $16 per person.

Scandinavia: In Denmark, about 400 restaurants featuring the DanMenu offer a two-course meal, lunch or dinner, for less than $10. In Norway, hotel rates range from $70 to $160 a night (for two people). Three Swedish cities -- Stockholm, Go teborg and Malmo

-- have put together packages that included accommodations plus a tourist card for free admission to attractions and free bus and subway travel. In Stockholm, the package is available at 50 hotels at $48 to $114 a night (for two people). The packages are available through Aug. 16 and on weekends thereafter. For information: Scandinavian Tourist Board, 655 Third Ave., New York, N.Y. 10017, (212) 949-2333.

Portugal: In the economy category, hotels range from $26 to $42 a night (for two people) and from $30 to $110 in the medium-priced category. Portugal's network of 30 pousadas -- very special lodgings in historic structures -- range from $44 to $88 a night. Dinners are $10 to $15 per person.

Greece: Rooms average $30 to $50 a night (for two people). A full dinner may cost as little as $6 per person. A full banquet for two, perhaps in view of the Acropolis, is about $50.

For a traveler on a budget, the fluctuating dollar calls for careful attention to currency exchange strategies.

When the dollar could go up or down while you are abroad, "It's always wise to hedge in both directions," says Otto J. Ruesch, president of Ruesch International Monetary Services, a currency exchange house in Washington. Ruesch advises travelers to Europe this season to carry 50 percent of their travel money in U.S. dollar travelers checks and 50 percent in the travelers checks of a strong European currency, such as Swiss francs.

"If the dollar depreciates," he says, "you have Swiss francs that appreciate." You use the U.S. dollar checks when the dollar strengthens; if it weakens, you use the Swiss franc checks. His firm is among those that sell U.S. and foreign currency travelers checks in the United States without charging a commission on the transaction.

For convenience, you also may want to purchase some foreign currency notes before you leave home. This allows you to familiarize yourself with the money, and you will be able to pay for a taxi or bus into the city without stopping at a foreign currency exchange booth when you land at the airport.

On the far side of the Atlantic, travelers also should be aware of exchange commissions that may be charged. Though he should know better, Ruesch says, he recently converted a $100 travelers check into British pounds at a bank in London without asking about the commission. The bank imposed a fee of three pounds or about $5 for the transaction.

Ruesch advises travelers to shop around for the best exchange rate, since the rates vary. Banks, rather than stores or hotels, offer the best rate -- usually better also than exchange booths at the airport. But you should also make a point of determining the commission, so you won't be as rudely surprised as he was.

With the dollar in a slump, you should also be careful about using credit cards for large purchases. You could lose on the exchange rate if the dollar declines before your purchase is converted to U.S. dollars for billing, sometimes a matter of several days or more.

Ruesch distributes two free pamphlets for travelers going abroad -- a U.S. dollar/foreign currency conversion guide (updated to exchange rates as of July 1) and a brochure detailing tips on how to avoid foreign currency hassles. Both are available by sending a stamped, self-addressed envelope to Foreign Currency Guide, Ruesch International, 1140 19th St. NW, Washington, D.C. 20036.