In a move that could prove to be a shot in the arm for President Bush’s $674 billion economic package, Sen. Zell Miller (D-Ga.) is set to announce that he will serve as a lead co-sponsor of the president’s plan.

Miller, who is retiring when his term expires in 2004, will publicly endorse Bush’s tax-cut proposal Thursday when the president visits Atlanta to deliver an economic speech, several sources said.

Miller and then-Sen. Phil Gramm (R-Texas) were the two primary sponsors of Bush’s $1.6 trillion tax cut proposal in 2001. With Gramm now retired, Senate Budget Chairman Don Nickles (R-Okla.) is expected to join Miller as the lead co-sponsor on the Senate bill.

Miller is the first Senate Democrat to back the president’s new economic plan, which is anchored by the elimination of double taxation on stock dividends and contains additional child tax credits, tax incentives for small businesses, and immediate reductions in individual income tax rates.

Since being appointed and then elected in 2000 to fill the remaining four years of the late Sen. Paul Coverdell’s (R) term, Miller has frequently sided with Bush on issues ranging from homeland security to judicial nominations. But it is his support for Bush’s tax cut in 2001 that angered many Democrats, who now suggest those cuts are, in part, responsible for sending the economy into a downward spiral.

“There he goes again betraying Senator [Thomas] Daschle [D-S.D.],” snapped a senior Senate Democratic aide. “The good news is it doesn’t look like he is going to bring very many Democrats with him this time.”

In fact, several key centrist Democrats who supported Bush’s plan in 2001, such as Sens. John Breaux (La.) and Ben Nelson (Neb.), have refused to endorse the president’s latest tax-cut proposal. Centrists in both parties have raised concerns about the price tag of the plan at a time of soaring budget deficits.

Bush’s 2001 tax-cut plan was eventually scaled back to $1.35 trillion and Miller led 12 Democrats, including Breaux and Nelson, in voting for it.

In recent months, Miller has made no attempt to hide the fact that he would continue to support Bush’s tax-cut plans in the 108th Congress.

“On the economy, I’m going to support each and every tax cut that comes before the Senate,” Miller said in a statement released after Bush’s Jan. 28 State of the Union address. “Like with my grandchildren, I love them all.”