Two million active and retired federal workers who have already waited 8 months for health premium refunds will have to wait even longer if budget cutters can persuade the president to veto the refund bill on his desk.

The president has until Monday to act on the bill, H.R. 3384.

The noncontroversial part of the bill would give retirees the same refunds -- ranging from $20 to $400 -- on 1985 premiums as those already approved for active-duty workers. More than half of the $1 billion-plus in refunds would go to the government. Plans offering the refunds say their 1985 costs dropped dramatically because people either didn't use their insurance as much as anticipated, or paid a bigger share of their own medical bills.

More than 250,000 people here are entitled to refunds if they had policies last year with Blue Cross-Blue Shield, Aetna, Government Employees Hospital Association, Government Employees Benefit Association, Foreign Service health plan, the American Federation of Government Employees or the National Association of Letter Carriers.

President Reagan approved the refunds last year, but the Justice Department said Congress would have to approve refunds for retirees. The insurance companies said they would wait until refunds for retirees were approved before sending out the checks to anyone, including active-duty workers. The Office of Personnel Management endorsed the refunds and Congress approved them in mid-December.

But some staffers at the Office of Management and Budget have warned that the second part of the refund bill -- the part raising the government share of health premiums -- could wind up costing Uncle Sam a lot of money.

The government now pays about 61 percent of the average employe's or retiree's health premium. Under the bill, the government share of the health premiums for many employes in low-cost plans would increase beginning in April. One federal official estimated that the change could cost the government as much as $89 million during this fiscal year.

That could be a problem because of the Gramm- Rudman-Hollings deficit reduction act, which mandates major federal spending cuts each year through 1991. Many of those cuts will likely be made from civil service salary and benefit programs.

"The cost issue has been raised by the OMB," said an OPM official. If the president vetoes the bill, OPM is expected to push for another bill that deals strictly with refunds and leaves out higher government health insurance payments.

"People will still get their refunds," predicted the OPM official. "It just could take a little longer."