President Clinton plans to offer his own version of a plan to guard surplus Social Security funds for the nation's retirees, a senior White House aide said yesterday.

The House has already passed a "lock box" for Social Security funds, which would prevent them from being tapped for uses other than for the retirement system, except in an emergency and only after a special vote of Congress. The Senate has been considering an even more stringent lock box to prevent the government from spending excess Social Security funds.

"Shortly, the president will put forward a strengthened Social Security lock box proposal that we think will be stronger than anything that has been proposed so far," Gene Sperling, director of the White House National Economic Council, said on CNN's "Late Edition."

The White House and Republicans in Congress are in a contest to demonstrate their commitment to protecting Social Security, which is running surpluses that are expected to disappear in about 10 years as the baby boom generation begins to retire.

Sperling did not offer any details of Clinton's proposal but said the White House hoped it would garner support from both Republicans and Democrats. Some congressional Democrats have criticized the lock box idea, saying it would not do much to address the long-term problems facing Social Security.

"We are very hopeful that the new presidential proposal -- that new Social Security lock box -- will be a way of bringing together both Democrats and Republicans," he said.

On Tuesday, Clinton plans to unveil a proposal for overhauling another large and popular program for the elderly: Medicare.

He intends to propose adding a prescription-drug benefit to Medicare, something that is not now offered.