PORTLAND – Maine’s tourism industry had its ups and downs last year, with overnight trips to the state showing a 4 percent rise, to more than 10 million, while day trips declined by 9 percent, according to newly compiled figures.

2006 marked the second year in a row in which overnight visits were up, reversing a four-year slump. But because this summer season appears to have gotten off to a slow start, there’s concern about whether the positive trend will continue.

Experts say the improvement reflects an expanding economy, better advertising and promotion, and the strong Canadian dollar. The reasons for the drop in day trips were unclear, but rising gasoline prices may have been a factor.

The figures were contained in an executive summary of the annual visitor study prepared by the Canadian research firm Longwoods International for the Maine Office of Tourism. Complete data, including benchmarks for spending on meals, lodging and other services, should be ready later this month.

The study found that despite efforts to lure tourists to Maine’s inland lakes and mountains, the most visited destinations were along the coast. The top nine, in descending order, were Portland, Kittery, Bar Harbor-Acadia National Park, Ogunquit, Freeport, Rockland-Rockport, Kennebunkport, Old Orchard Beach and Boothbay Harbor.

Maine’s share of overnight travelers nationally and in the Northeast edged up last year, returning to 2001 levels for the first time since the Sept. 11 terrorist attacks, according to Charles Colgan, associate director of Maine’s Center for Tourism Research and Outreach.

Overnight trips continued to rise because gasoline prices don’t prompt people to cancel vacations, Colgan suggested, but they may think twice about driving to Maine to shop in Kittery or Freeport, for example.

“Day trips are marginal trips,” Colgan said, whereas overnight visitors spend an average of four days in the state and spend the most money, on lodging, food, shopping and other things.

The preliminary Longwoods data indicate that the state’s advertising and promotion efforts are bringing results, said Patricia Eltman, Maine’s new tourism director. The agency has been expanding its advertising in Philadelphia and Washington, D.C., while continuing its longstanding media buys in New York and Boston.

Vaughn Stinson, executive director of the Maine Tourism Association, expressed concern that midweek bookings at motels and campgrounds are lower than usual this summer and that inland areas such as the Moosehead Lake and Rangeley Lakes regions are reporting slower-than-normal business.

“It’s not a robust season by any means,” he said.