Americans who put off vacations last year plan to hit the road in '83

After sitting home last summer and worrying about the economy, Americans are getting ready to head out this year. Encouraged by a recovering economy and slower increases in travel costs, an estimated 119 million Americans will take summer vacation trips, a 14 percent increase over last year, according to projections from the United States Travel Data Center.

''People did not cancel (last year's vacation) trips willy-nilly, they postponed them,'' center director Douglas C. Frechtling explains. ''And the economy has improved, (providing) the financial resources for the consumer to act on his dreams.''

Not only will more people travel this summer, they will take more individual trips. The total number of trips is expected to increase 12 percent over last summer, to 292 million. That's the largest increase since 1978, according to the center, an industry-sponsored research group.

The most popular destination: Walt Disney World in Orlando, Fla. ''There is nothing in the world'' that attracts as many vistors for a prolonged stay, Mr. Frechtling says.

With vacationers eager to see the park's EPCOT (Experimental Prototype Community of Tomorrow) area, attendance soared 102 percent, to 10.6 million, in the six months ending last June, according to Disney spokesman John Dreyer. This summer some 13 million travelers are expected to visit.

Of course, consumers may fool travel forecasters by saying one thing and then doing another. Such a shift could occur if, for example, economic indicators suddenly grew gloomy. Last year, for example, the center surveyed consumers and then used an economic model to predict that the number of vacation trips would rise 4 percent. But people actually cut the number of their trips by 9 percent.

''Consumers suddenly lost faith in the recovery,'' Mr. Frechtling explains.

And potential travelers have been sending some mixed signals this year, too. The American Automobile Association reports that requests for travel assistance materials are up only 1 percent from last year.

''We see a modest increase in (automotive) travel, not a big banner year,'' an AAA spokeswoman says. But she cautions that the actual pattern is difficult to predict until after the Memorial Day holiday.

One reason information requests to the AAA may be lagging is that consumers are feeling better off and plan to increase their use of air travel. Even though gasoline prices fell 9.2 percent in the 12 months ending in March, slightly more Americans plan to travel by plane than car this summer.

Roughly 85 percent of the summer vacation trips will be made by car or truck, vs. 86 percent last year. Meanwhile 11 percent of the trips will be made by air, vs. 10 percent last year.

''Apparently financial perceptions have generated a desire to travel farther from home, requiring more air travel,'' according to the center's report on the summer travel outlook.

Travelers' increased confidence in their finances can also be seen in lodging plans. This summer only 39 percent of the vacation trips will include a stay with friends or relatives, as against 41 percent of the trips made last summer.

That may be welcome news for hosts, since the number of nights spent on the road is expected to climb 19 percent this summer to 1.633 billion. And the average trip length is expected to increase 6 percent, to 5.59 nights.

Reduced inflation in travel costs is one reason longer trips will be possible. In the 12 months ending in March, lodging costs rose 4.7 percent, compared with an 11.8 percent increase the previous year.

And airline fares rose 6.3 percent in the 12 months ending in March. There was a 10.3 percent increase the previous year. In fact, as a result of lower gasoline costs, overall transportation prices fell 1.2 percent in the year ending in March.

Americans' travel plans differ significantly according to where they live. The biggest increase in vacation travel will take place among residents of the Northeast, who plan to make 24 percent more trips this summer than last. One reason for the increase is that several states in the region have declining unemployment rates. The Northeast is also expected to be the most popular regional destination for travelers, with the number of trips projected to rise 20 percent.

By contrast, residents of the South plan to take 6 percent fewer trips this summer than last. It is the only region where the number of vacation trips by residents is expected to fall. Unemployment in the area has increased in the past year and travel in the region will not receive the stimulus it did last year from the World's Fair.