More American and international travelers than ever are seeing the U.S.A. this summer -- if not in their Chevrolets, then by plane, train, bus or recreational vehicle, according to travel industry reports.

The third-straight year of record U.S. travel is being spurred by a stable economy and more leisure time for American vacationers and a record number of international visitors attracted to the United States by favorable dollar-exchange rates, according to the Travel Industry Association of America's summer travel study.

"If the trend continues as expected, 1987 will break all records and be the best year ever for travel in the U.S.," said William D. Toohey, TIA's president.

For the summer alone, vacation trip volume is expected to increase 4 percent over last summer, to a record 297 million trips of 100 miles or more from home, according to the U.S. Travel Data Center, TIA's research arm.

"It's a very good year, no question," said Dan Bohan, owner of the Washington area's largest chain of travel agencies, Omega World Travel. "June was just tremendous," said Bohan, citing a healthy economy and the rising importance of leisure time to Americans.

And if vacations are becoming increasingly important to Americans, it may be because they are following the example of their cousins abroad, who have always ranked a visit to the United States as a top priority. The U.S. Travel and Tourism Administration expects the number of international travelers coming to the United States to reach 24 million this year, an increase of nearly 4 percent over last year.

In addition to the general economic well-being of many Americans, the relatively stable costs of transportation, food and lodging for travelers has encouraged more vacationers to spend more time away from home, TIA said. The index of travel prices is projected to increase 3.5 percent for such costs, TIA said, the same as the overall consumer price index.

This year, with no outstanding draws such as a Statue of Liberty celebration, travelers are returning to the traditional vacation destinations, according to industry experts. Florida is still the number one summer vacation destination, while Hawaii is the location whose popularity is increasing fastest, according to an American Express Travel-Related Services survey. San Francisco, Las Vegas and New York are the most popular U.S. cities, the survey showed.

During the benchmark July 4th holiday, 35 million Americans, or nearly 15 percent of the population, took a trip of 100 miles or more away from home, according to the American Automobile Association, an increase of 6 percent over last year. And, in spite of gasoline prices that are inching up over the $1 mark for the first time in a year, travel by car is on the increase.

"It's not a serious deterrent to vacation travel," Richard Hebert of AAA said of the rising gasoline prices. "It's still relatively inexpensive compared to a few years ago," he said, adding that, with more fuel-efficient cars, consumers are more concerned about gas supplies -- which have been plentiful -- than costs.

There is no indication that the recent spate of frustrations and delays in air travel have kept vacationers from flying. Traffic on U.S. carriers rose 13.8 percent in the first six months of this year, and was up 11.6 percent in June alone, according to the Air Transport Association of America.