Washington ? The Senate unanimously agreed Tuesday that strengthening Social Security was “a vital national priority” but split acrimoniously along party lines on what to do about it in the first votes on President Bush’s plans.

In one exception to the party divide, five Republicans broke ranks and voted with the Democrats in favor of a resolution declaring, “Congress should reject any Social Security plan that requires deep benefit cuts or a massive increase in debt.”

Democrats argue that Bush cannot establish private investment accounts, his signature proposal for revamping the retirement program, without cutting benefits or adding to the federal budget deficit.

“They’re nervous. They’re worried. But their hands are tied as long as the president sticks to privatization,” said Sen. Charles E. Schumer of New York, the top Democratic spokesman on the issue in the Senate.

The vote on the resolution, offered by Sen. Bill Nelson, D-Fla., was 50-50, with Republicans Susan Collins and Olympia Snowe of Maine, Mike DeWine of Ohio, Lindsey Graham of South Carolina and Arlen Specter of Pennsylvania joining with the chamber’s Democratic minority.

Senate Budget Committee Chairman Judd Gregg, R-N.H., told Democrats that rather than offering a plan for overhauling the giant pension program, “You just put out there amendments which are for the purposes of political protection. You should be ashamed of yourselves.”

The resolutions voted on Tuesday were nonbinding.