WASHINGTON — The State Department urgently needs to overhaul the way it handles passport applications to avoid a repeat of the massive backlogs last summer that frustrated countless travelers, congressional investigators concluded.

They said the department must develop a "comprehensive, long-term strategy" to meet rising demand for the identity documents. The Associated Press obtained a draft copy Thursday of the report by the Government Accountability Office, the investigative arm of Congress, ahead of its expected release today.

Lawmakers asked for an investigation into the backlog that swamped passport offices last spring and summer, the result of a record 18 million applications.

"The 2007 surge in passport demand exposed serious deficiencies in State's passport issuance process. Passport wait times reached record highs, leading to inconvenience and frustration for many thousands of Americans," the report found.

The department "needs to rethink its entire end-to-end passport issuance process, including each of the entities involved in issuing a passport, and develop a formal strategy for prioritizing and implementing improvements to this process," according to the investigators.

The need for such a strategy is urgent, they said, because the demand for passports is expected to keep soaring in the coming years.

Investigators also recommended creating a system to track individual passport applications as they are handled. That would make it easier for applicants and government workers to track their progress.

Department officials have acknowledged underestimating the high demand for passports last year, but said it was a historic change in behavior by Americans that was not predicted.

The report found a number of crucial missteps or misjudgments that led to the passport mess:

* A department study used to estimate future passport demand failed to account for a large group of likely travelers.

* When the backup began in early 2007, officials did not realize how large it was. They were unaware that many applications were piling up at the offices of a private contractor handling the initial paperwork.

* As the typical four-week wait for a passport turned into 12 weeks or more, officials could not quickly locate specific applications.

The delays led to long lines at government buildings. Lawmakers held hearings after their offices were swamped by requests from constituents desperate to make a long-planned family trip or holiday.

Under intense criticism, the department ordered mandatory overtime, brought some employees home from foreign posts to help, and sped up hiring.

The GAO found those measures worked well to alleviate the backlog. But they said the department took a "day-to-day" approach to the problem rather than overhauling and re-examining the entire process.

By last October, the wait times had come back down to normal levels, and this summer's batch of applications has gone smoothly. The department's Web site says people can expect a passport application to be processed in about four weeks.

Some of the demand for new passports resulted from new travel rules that required U.S. citizens to have a passport when returning from trips within the Western Hemisphere, including Canada and Mexico.

Lawmakers fear another round of travel headaches next year, when passports will be required of every American citizen driving back across the northern or southern U.S. border.