Georgia Sen. Zell Miller (search), the highest profile Democrat to endorse President Bush for re-election, will speak at the Republican National Convention (search) later this summer, a congressional aide said Friday.

Miller drew a sharp rebuke from the dean of Georgia's congressional delegation, Democratic Rep. John Lewis, who called the senator's decision "a shame and a disgrace."

According to the aide, who spoke on condition of anonymity, Miller will give his address on Wednesday night of the four-day convention in New York that begins Aug. 30. The Bush-Cheney campaign was expected to make an official announcement later in the day.

The speech by Miller, a former two-term governor, comes 12 years after he delivered the keynote address for Bill Clinton at the 1992 Democratic National Convention, also held in New York.

Miller, who is retiring in January, has voted with Republicans more often than his own party and has been a key sponsor of many of Bush's top legislative priorities, including the Republican's tax cuts and education plan.

In May, Miller spoke at the Georgia Republican convention and criticized Democratic presidential candidate John Kerry as an "out-of-touch, ultraliberal from Taxachusetts" whose foreign and domestic policies would seriously weaken the country.

"I'm afraid that my old Democratic 'ties that bind' have become unraveled," Miller said.

In 2001, Miller had told a Georgia Democratic Party gathering that Kerry, the four-term Massachusetts senator and decorated Vietnam War veterans, was "an authentic" American hero who had worked to strengthen the military.

Miller's recent book, "A National Party No More: The Conscience of a Conservative Democrat," is now a national best-seller. In it, he assails members of his own party, including Clinton.

"I think he has sold his soul for a mess of pottage," Lewis said, a reference to a speech Miller gave 40 years ago in which he argued that President Johnson was abandoning his Southern roots by pushing some civil rights issues. Pottage is defined as a thick soup or stew of vegetables.

Bobby Kahn, the chairman of the Georgia Democratic Party, said he wasn't surprised.

"Maybe I'll switch to the Republican Party so I can speak at the Democratic Convention and bash Bush," Kahn said. "It makes about as much sense."

Kahn was a top aide to Democratic Gov. Roy Barnes, who appointed Miller to the Senate following the death of Miller's predecessor, Republican Sen. Paul Coverdell.

"I advocated his appointment," Kahn said of Miller. "He said he would be independent and he was for a while, but he hasn't been lately. He's been in lockstep with the Republicans and I don't know what's happened to him. It's really kind of sad."