Washington ? Struggling with a deluge in passport applications, the State Department did what much of the government does to deal with a manpower crunch: It hired more private contractors.

But the practice of outsourcing allowed hired hands to snoop around in presidential candidates’ files. And now it’s pointing to questions about whether outside contractors should have access to such sensitive information about any citizen.

The government routinely relies on private firms to do sensitive work – from managing weapons systems to protecting traveling diplomats to helping maintain records that contain private information on U.S. citizens. The Bush administration in particular has embraced the practice of outsourcing as a way to save money and improve efficiency, particularly in Iraq where there are just as many defense contractors as there are service members.

With the influx of contractors come increasing questions about lack of control.

The State Department, for example, has had to defend its employment of private security guards after several Blackwater Worldwide employees were involved in shootings that left Iraqis dead.

Then, last week, contractors were found to have pried into the passport files of Democratic presidential candidate Barack Obama and Republican rival John McCain. Two contractors were fired and a third disciplined.

Democrat Hillary Rodham Clinton’s files also were breached when a State Department employee used the senator’s name during a training session and was reprimanded, officials said.

The State Department’s inspector general is expected to determine whether the files of other high-profile people were breached and if the searches involving the presidential candidates were politically motivated.

Spokesman Sean McCormack said Monday that the Justice Department has an “open invitation” to become involved. Attorney General Michael Mukasey has indicated that prosecutors are likely to wait until the assessment concludes before deciding whether to open an investigation of their own.

In the meantime, McCormack said the agency isn’t concerned it might be relying too much on private firms to help issue passports. The State Department’s Office of Passport Services employs about 2,600 contractors nationwide. “These contractors go through vigorous personal integrity tests, the same kinds of tests that career government employees undergo,” he said.

Last year, the number of passport application requests soared after the January implementation of new rules that required air travelers from Canada, Mexico, the Caribbean and Bermuda to present passports. The State Department went from issuing some 12 million passports in 2006 to 18 million in 2007.

As the backlog worsened, the State Department took drastic and expensive measures, even paying some employees to return to the U.S. from overseas to help handle the paperwork. Anticipating the influx of requests to continue, the department hired contractors too.

It remains unclear as to exactly what the contractors might have seen. Passport applications typically contain only basic personal information such as name, citizenship, age, Social Security number and place of birth. The files generally would not list countries the person has traveled to, agency officials said.

However, Passport Services maintain other records too, according to a Jan. 9 notice in the Federal Register. The federal notice says such information such as marriages overseas, court orders, arrest warrants and medical and financial reports may also be contained within the system.