Washington ? Massachusetts Democrat John Kerry, a leading Senate liberal and decorated gunboat officer during the Vietnam War, said Sunday he is taking a first step toward running for president in 2004.

He took aim at President Bush’s policies on taxes, education, Iraq and the Middle East, saying, “There is a better choice for this nation.” Bush, asked Sunday night about the prospect of running against Kerry, smiled at reporters but said nothing.

Kerry, a 58-year-old former prosecutor first elected to the Senate in 1984, has said for the past year that he was seriously thinking about a run in 2004. He was unopposed for re-election in November to a fourth term :quot; the first Massachusetts senator in 80 years with no major-party opposition.

“I’m going to file this week an exploratory committee, a formal committee, and I’m going to begin the process of organizing a national campaign,” Kerry said on NBC’s “Meet the Press.”

An official announcement of his candidacy is months away, Kerry said.

Exploratory committees are established by budding candidates mainly to raise money, finance travels around the country and help gauge voter support.

Democrats are expected to have a crowded field of candidates, with the party convention to be held in Boston.

Vermont Gov. Howard Dean already is running. Former Vice President Al Gore, the 2000 nominee, and North Carolina Sen. John Edwards expect to disclose their plans after the Christmas holidays. Outgoing House Democratic leader Dick Gephardt of Missouri is expected to begin telling colleagues whether he plans to run. Also considering the race is Gore’s running mate from two years ago, Sen. Joseph Lieberman of Connecticut, who has said he would not run if Gore does.

A recent Los Angeles Times poll of Democratic National Committee members showed Gore and Kerry topped lists when people were asked their favorites.

During the NBC interview, Kerry repeatedly mentioned his service in Vietnam. He was an officer on a gunboat in the Mekong Delta and received numerous decorations for his combat experience, including a Silver Star and three Purple Heart awards.

He later led demonstrations against the war after he returned home.

Kerry has been drawing differences with Bush in the areas of energy and foreign policy in appearances around the country. He plans to lay out his economic plan in a policy speech Tuesday in Cleveland, including focusing tax cuts more on the middle class.