CHICAGO — Tanned, rested and ready to rumble, Vice President Al Gore returned to the campaign trail Friday to energize traditional Democratic voters and head off Republican attempts to appropriate some of his party's core issues.

Before adoring audiences of union voters, Gore dismissed this week's Republican convention in Philadelphia as a "masquerade ball for special interests with a purpose," a play on the GOP convention theme of "prosperity with a purpose."

He also tried out a new refrain that is likely to become a campaign watchword: "They're for the powerful; we're for the people."

With the Republican presidential candidate, George W. Bush, leading his party toward the center, Gore's campaign is returning to the Democrats' populist roots and trying to revive the party's traditional coalition of blue-collar workers, liberals and minorities.

Borrowing the rhetoric of Republican President Abraham Lincoln, Gore told the convention of the International Fire Fighters Association that the Republican agenda was "of big oil, by big oil and for big oil," a reference to the fact that both Bush and running mate Richard Cheney were oil industry executives.

Responding to Republican attacks that Democrats failed to take advantage of the country's current prosperity, Gore ticked off a list of Clinton-Gore administration accomplishments, including the creation of 22 million new jobs and the elimination of the federal budget deficit.

"What planet have they been on?" Gore asked.

His speeches Friday before the firefighters and the National Association of Letter Carriers were his first public appearances since he spent a week vacationing on a North Carolina beach while the Republicans gathered in Philadelphia to nominate Bush.

His campaign rallies were bright, loud and pulsing with energy, designed to pump up both the faithful and the candidate, which they clearly did.

The packed ballroom at the Sheraton hotel in Chicago was a sea of bright yellow T-shirts emblazoned with "Fire Fighters Gore," vivid against a podium bathed in red and royal blue. When the vice president entered with his wife, Tipper, the hall exploded into an ovation that lasted more than seven minutes. The adulation was almost palpable. -->

"We've been with Al Gore every step of the way," said Alfred Whitehead, the outgoing general president of the firefighters. "The November election is only 14 weeks away. We're going to continue to work with Al Gore until the last poll closes."

The firefighters were the first union to endorse Gore, in January 1999, and the Gores have not forgotten.

"You were the first to fire it up!" Tipper Gore said, igniting another loud burst of cheering and applause.

Gore's performances Friday suggested he has responded to criticism that his campaign appearances have been too staged and mechanical, and not personal enough.

His first speech was a cogent blend of familiar Democratic rhetoric on the party's core issues, such as education and health care, and a smattering of anecdotes about his own life.

"I want people to know who I am," he said, then talked about his volunteering for Vietnam, where he served as an Army journalist, and his subsequent career as a newspaper reporter in Nashville, Tenn., before he entered politics.

Gore also seemed more relaxed than usual, and when he became animated, it seemed to come more from his heart than from a political script.

"It's not like he hasn't spoken before us before," said Jerry Robusto, a union member from Baltimore. "It just seemed like he was real charged up."

With Republicans in full throat now that their ticket has been set and their troops energized, Gore may need all that — and more.

"We're starting out behind," he told the union members, whose support and organization will be crucial to his campaign. "I know it's going to be a tough fight with powerful forces lined up against us."

His speeches Friday and one Saturday before a police officers association are dry runs for the next 12 days, a sprint across key states in the South and the Midwestern heartland that he needs to win in November.

Gore is set to name his running mate Tuesday in Nashville, then to campaign his way to the Democratic convention in Los Angeles, which begins Aug. 14.

He has narrowed the list of potential vice presidential candidates to six or seven, though in reality it may be much shorter.

"If I were him, I'd pick a vice president next week, then get him on a boat, plane, train for most of the next three months in the Midwest," said Rep. Tim Roemer, D-Ind.