WASHINGTON - The Secret Service has imposed a new, stricter policy that prohibits staff from driving government cars within 10 hours of drinking alcohol, according to an internal agency memo reviewed by the Washington Post.

The new policy was announced to staff Monday amid an inquiry into allegations that two agents drove through a secure bomb-threat investigation scene at the White House earlier this month after a party at a nearby bar. It replaces previous rules prohibiting staff from operating vehicles when they are under the influence of alcohol or perceived to be impaired.

The new rules were issued internally the day before Secret Service Director Joseph Clancy appeared before a House committee investigating the March 4 incident.

"Secret Service employees are responsible for conducting themselves in a manner that reflects the highest standards of the United States Government and must maintain an appropriate state of awareness and mission preparedness," says the Monday memo to staff.

The memo warned that employees who violate the policy will be "subject to the full range of available disciplinary and adverse actions up to and including removal from employment."

A Secret Service spokesman, Brian Leary, declined to discuss the new policy or say whether it was adopted in response to the March 4 episode. A government inspector general and lawmakers are investigating allegations that Secret Service officers on duty that night suspected the two agents were under the influence of alcohol but were ordered not to conduct sobriety tests.

"The Director will continue to update U.S. Secret Service policies as needed," Leary said via e-mail.

Clancy mentioned the rule change in passing during his Tuesday appearance in the House. He told lawmakers that, at the time of the March incident, agents were not allowed to drive a government vehicle under the influence of alcohol." Later, he added: "We've changed the policy. Driving - within 10 hours you cannot enter a government-owned vehicle or a leased vehicle. That policy has gone out. We revisited that."

The new rule on operating government vehicles follows policies imposed last year prohibiting special-operations staff from drinking alcohol within 12 hours of reporting for duty and 24 hours before the president's arrival at any trip location. Those rules were adopted in response to two cases of alleged alcohol-related misconduct by Secret Service employees ahead of visits by President Obama to the Netherlands and the Florida Keys.

On Thursday, a bipartisan group of House Judiciary Committee leaders and the chairman of the House Homeland Security Committee introduced legislation that they said was needed to reform the Secret Service.