High fuel prices have made running an airline a money-losing proposition so far this year, but the industry found a glimmer of sunshine Wednesday in a forecast that seats would be full and that a record number of people planned to travel internationally this summer.

The trade group Airlines for America (A4A) said domestic travel would remain flat this summer, with about 5 percent fewer passengers than the record high of 217.6 million set in 2007. Internationally, however, the estimated 26.8 million passengers would be about 500,000 more than any previous summer.

“Customers are benefiting from record airline operational performance and greater access to the global economy while fares continue to trail the price of other services,” A4A President Nicholas E. Calio said.

With fuel costs up about 19 percent over the same time last year, the industry had a net loss of $1.73 billion in the first quarter, A4A said.

United airlines reported a $286 million first-quarter loss, saying it spent $557 million more on fuel than it had in the first three months of 2011. United, which merged with Continental Airlines in 2010, is the dominant carrier at Dulles International Airport .

High fuel and labor costs helped push American Airlines into bankruptcy last year. As the airline’s management works to reorganize, US Airways has struck a deal with American’s unions in a first step toward promoting a merger between the two airlines.

The International Air Transport Association, the global sister to A4A, said airlines have lost $25 billion worldwide since 2001. IATA President Tony Tyler forecast that they would make a profit of less than 1 percent this year.

In its forecast released Wednesday, A4A said that from June through August, U.S. airlines will carry an average of 2.24 million travelers globally every day. Domestically, 179.4 million passengers are expected to fly this summer.

“With fuel at record-high levels, the financial loss suffered in the first quarter would have been substantially deeper if not for the significant proactive steps that the airlines have taken,” A4A chief economist John Heimlich said.