The Missouri lawmaker, who has stepped aside as House minority leader, filed papers Monday establishing a presidential exploratory committee.
"On nearly every issue of importance to the country — national security, the economy, health care, education, energy policy — President Bush is leading the country either down the wrong path or not leading at all," Gephardt said in a written statement earlier.
The 61-year-old congressman said he would offer a "different direction for our domestic, economic and national security policies."
Exploratory committees are established by candidates mainly to raise money, finance travel and help gauge voter support.
White House officials said Mr. Bush's focus is on waging the war on terror, on defending the U.S. homeland and on strengthening America's economy. The administration, they say, is making steady progress in all areas.
Already saying they will seek the Democratic nomination are Vermont Gov. Howard Dean, Massachusetts Sen. John Kerry, North Carolina Sen. John Edwards and the Rev. Al Sharpton of New York.
Senate Democratic leader Tom Daschle of South Dakota and Connecticut Sen. Joseph Lieberman appear poised to enter the race.
Daschle said Sunday he's strongly considering a run.
"I think it's fair to say I'm leaning in the direction of offering my candidacy for president," the senator said after a meeting with constituents this weekend.
Daschle spent the weekend talking with supporters in Rapid City, Aberdeen and Sioux Falls and said an announcement on an exploratory committee is likely "in the next couple of weeks."
Daschle said if he runs, he'd stay on as Democratic leader. "I think that our caucus needs that stability and my expectation is that I would be leader for the foreseeable future."
Gephardt named S. Lee Kling of St. Louis, a leading fund-raiser for Democrats over the years, as treasurer of his exploratory committee.