New rules for a merit pay system at the Homeland Security Department (search) won cautious support Thursday from congressional investigators who also urged the agency to explain how the change would be carried out.

The department needs to make sure that "sustained and committed" managers and a strong communications strategy are in place, the Government Accountability Office (search) said in a report released Thursday.

"The regulations contain many of the basic principles that are consistent with proven approaches," the report said.

The regulations, set to be phased in over several years, are intended to attract and reward high-performing employees, and give agency managers broad authority to change workers' shifts and duties without delay.

Unions representing the 110,000 employees who would be affected say the change would limit their collective bargaining rights.

The department says the regulations preserve collective bargaining rights for workers. But a department fact sheet to employees states the regulations "expand the number of situations in which we will no longer bargain with employee representatives, and place time limitations on other areas where we will continue to engage in collective bargaining."

The unions sued last month to block the regulations. In a related matter, the American Federation of Government Employees (search) filed suit Thursday against similar rules recently approved at the Defense Department that would affect about 750,000 employees.

Gordon England, the Pentagon official who has overseen the development of the proposed new work rules for defense civilians, said at a news conference that they would provide a "much more flexible and agile system" that rewards performance more than longevity. Defense Secretary Donald H. Rumsfeld has promoted the changes as essential to transforming the Defense Department into a modern organization.