Entering a crowded Democratic field, the Missouri lawmaker promised to deliver health insurance to "everyone who works in America."
Gephardt, 62, also sought to distinguish himself from lesser-known Democratic rivals by embracing his long record in politics. "I think experience matters," he said in a text of his address. "It's what our nation needs right now."
"I'm not the political flavor of the month. I'm not the flashiest candidate around," said Gephardt, whose 1988 presidential campaign fizzled after winning the Democratic caucuses in Iowa. "But the fight for working families is in my bones."
Surrounded by friends and family in the gymnasium at his former elementary school, Gephardt said, "I love America. I know we can do better. I know we can do more. Here in the home of my values, here at the heart of the American dream, I announce my candidacy for the president of the United States."
While saying he supports Mr. Bush's efforts to disarm Iraq, without the United Nations if necessary, Gephardt said the president's go-it-alone rhetoric has alienated allies.
"We must lead the world instead of merely bullying it," he said as Bush wrestles with skeptical allies over his plans for a possible war in Iraq. Last fall, despite objections from many House Democrats, Gephardt worked closely with the Bush administration in drafting the congressional resolution authorizing the use of force to oust Iraqi President Saddam Hussein.
"I'm running for president because I'm tired of leadership that's left us isolated in the world, and stranded here at home," he said.
Gephardt, the son of a milk truck driver who belonged to the Teamsters, returned home in an effort to soften his public image and argue that his roots shaped his political career.
He accused Bush of presiding over "the economics of debt and regret," and called White House tax cuts "unaffordable, unsustainable and patently unfair."
He blasted Bush's education, environmental, budget and homeland security policies, then said: "Never has so much been done, in so little time, to help so few."
Seven other Democrats already have formed presidential committees or say they intend to do so: former Illinois Sen. Carol Moseley-Braun, former Vermont Gov. Howard Dean, Sen. John Edwards of North Carolina, Sen. John Kerry of Massachusetts, Rep. Dennis Kucinich of Ohio, Sen. Joe Lieberman of Connecticut and New York civil rights activist Al Sharpton.
Moseley-Braun and Kucinich were expected to take the first step toward a formal campaign by announcing the formation of exploratory committees Wednesday, or later this week, depending on when the Federal Election Commission reopened in snowbound Washington.
Others are considering bids, including Sens. Bob Graham of Florida, Christopher Dodd of Connecticut and Joe Biden of Delaware, along with retired Gen. Wesley Clark and former Colorado Sen. Gary Hart.
Dean, Edwards, Gephardt, Kerry and Lieberman have gained distance from the rest of the pack thus far, either by simple name recognition, frequent travel or strong early efforts to organize in key states.
In his speech, Gephardt said he would "put hardworking Americans first again," an echo of former President Clinton's 1992 "putting people first" campaign slogan.
He pledged to start with health care reform and pension protection.
"Without the Bush tax cuts for the wealthy, we can finish the unfinished business of providing high-quality health coverage to everyone who works in America — saving billions, and stimulating one of the biggest sectors of our private economy," Gephardt said.
He outlined a plan to give employers tax credits that would cover "most of the cost" associated with providing health care coverage to their workers. With the new incentive, businesses would be expected to offer health care coverage to full-time workers, aides said.
They said the plan, which will be detailed in a separate speech later this year, could eventually cost as much as Bush's 10-year, $1.3 trillion tax cut plan.
The health care initiative is the cornerstone of an ambitious policy agenda designed to win what Gephardt called "the contest of ideas." It is his answer to critics who say other Democratic candidates have more momentum or charisma.
As House minority leader, Gephardt ran the Democratic House campaigns in 1996, 1998, 2000 and 2002 — gaining some ground but never seizing control from Republicans. Two days after Democrats lost seats in November, he resigned his leadership post amid criticism from party activists and began to plot his White House bid.
The sandy-haired youthful-looking Gephardt has built a formidable fund-raising network as House minority leader.
Years of unrelenting campaign travel for Democratic candidates, plus his own 1988 presidential bid, brought Gephardt in contact with scores of party activists, many of whom owe him a favor or two.
His opposition to trade agreements has won the praise of labor leaders, though their endorsements this year are far from assured.
But many Democrats wonder whether Gephardt has grown stale and unable to excite activists. They are looking for assurances that he could beat Bush.