Staff at the U.S. Naval Research Laboratory in Washington spent more than 9,000 hours over five months last year preparing and reviewing requests from scientists and engineers to attend conferences and present research. The tab for taxpayers: $824,000.

The Energy Department's Los Alamos National Laboratory in New Mexico spent $1.6 million to review similar travel and conference requests during one fiscal year, an increase of $1.4 million from the previous one.

And Los Alamos officials poured $708,500 into updating a travel and expense management system so that they could track all the paperwork.

These expenses are among the extraordinary costs that federal agencies say they have incurred in the three years since the Obama administration severely clamped down on employee travel to training and other conferences, after a Las Vegas spending scandal.

The Government Accountability Office identified the examples in a study this month of the 2012 policy's effects on science, technology, and engineering researchers at the Departments of Defense and Energy, which employ more than 129,000 of these experts.

The GAO, the watchdog arm of Congress, concluded that travel restrictions at the two agencies have severely curtailed attendance at academic conferences, a frustration felt by employees across the federal government.

The scientific community, which complained early on to Congress and the White House that the travel curbs were diminishing government researchers' standing in the United States and abroad, was hit particularly hard.

With only shaky assurances that their supervisors will approve their attendance at a conference with a reasonable lead time - or approve the request at all - "scientists and engineers are less likely to submit papers or accept speaking invitations," the GAO found in its 52-page report.

"They do not have assurance that a decision regarding attendance will be made in a timely fashion, DOD and DOE officials told us, because they may be concerned about their standing with peers in their technical communities," auditors found. As a result, the departments are worried about recruiting top talent and keeping scientists from leaving for academia or industry jobs.

But the report offers new details on the tangible costs to taxpayers of implementing the travel restrictions, which came after embarrassing revelations by the inspector general for the General Services Administration. Three hundred employees in the GSA's Public Buildings Service took a four-day junket in Las Vegas that featured a mind reader, after-hours parties in loft suites, and a bike-building exercise. Lavish conferences held by several other agencies soon came to light.

Although the government has not released data on how much agencies spent on travel and conferences before the crackdown, White House officials have said the restrictions have saved about $3 billion and have ensured that taxpayers are not paying for more boondoggles.