Democratic Party leaders said yesterday they plan to make their nominating convention in Boston later this month a four-day reintroduction of Sen. John F. Kerry, enlisting his wife, children and former war comrades in Vietnam to make the case for a man they acknowledge remains an opaque figure for millions of Americans.

"Stronger at Home, Respected in the World," is the theme of the Boston event, said Democratic National Committee Chairman Terence R. McAuliffe. The phrase is designed to underscore the centrist and forward-looking image Kerry wants to present to voters -- an implicit attack on President Bush and a rebuttal to Bush's argument that Kerry would be a weak and irresolute commander in chief.

Kerry's acceptance speech on July 29 is likely to be the most important event of his candidacy before the fall debates, and he will be introduced by his two daughters; his crewmates in Vietnam, where he commanded a Swift boat; and former senator Max Cleland (Ga.), who lost three limbs in that war.

This battle over biography -- who is Kerry and what does he stand for? -- is at the heart of the convention, strategists in both parties said yesterday. A successful event, they said, would refashion Kerry from someone still defined more heavily by who he is not -- Bush -- than by his career as a veteran, former prosecutor and a senator with a two-decade record that he says bolsters his claim that he would be an effective advocate for ordinary Americans.

Even a carefully choreographed convention, however, presents ample opportunity for failure, according to strategists experienced in this distinctive quadrennial ritual of American politics. Among the hazards, particularly in the current highly polarized political environment, is that some on the roster of speakers -- a list that includes former president Bill Clinton and former vice president Al Gore on the opening night, July 26, and Sen. Edward M. Kennedy (Mass.) the next night -- will use their moment to deliver partisan invective that will thrill the audience inside Boston's FleetCenter but could strike the television audience as too strident.

Another is that Kerry will fumble his prime-time opportunity with an acceptance speech that echoes some of the flat performances he has given on the campaign trail this year.

Convention success is measured by the numbers. Historically, effective conventions have produced a "bounce" for the nominee in polls of about 10 percentage points or more. This year, some Democrats maintain that wide swings are not possible, since surveys indicate a higher-than-normal percentage of the electorate has already chosen sides, leaving a smaller number of undecided voters.

Even so, strategists say Kerry's goal is obvious: to emerge from Boston and the extended national exposure a convention offers with an unambiguous lead over Bush. This will force Bush to have an equally successful Republican convention and public opinion bounce just to reach parity. On the other hand, if Kerry stumbles in Boston, Bush could use his convention in New York at the end of August to open up a commanding lead once the campaign homestretch begins on Labor Day.

"There's a lot of people who feel they don't know enough about John Kerry to make a judgment about him and his values," Kerry pollster Mark Mellman said. A successful convention, he said, will acquaint Americans with "a person who cares about family and faith and opportunity." But Mellman said it is unrealistic to expect a sizable shift in "the horse race numbers."

"Lines are hardened," he said. "He's already consolidated partisan support" -- something that traditionally happens at conventions -- "and there is not a lot of room to grow."

Mark Penn, a pollster for Clinton, said that if Kerry's support does not grow, it is a bad sign for him. Historically, he said, winning candidates receive a 12-point jump in their polling support, and even in a more polarized environment Kerry's aim must be a gain in numbers approaching double digits by the first week in August. Penn argued that Kerry has no more important event than his address on July 29, when the task will be to present himself as both a comfortable presence and a commanding one. For challengers, convention addresses amount to a "State of the Union" address.

"Seventy-five percent of the campaign for Kerry is that week, and the rest is holding on to the gain from that week," Penn added.

Scott Reed, a GOP strategist who managed Robert J. Dole's 1996 campaign, agreed with Mellman that this election has become a contest "about a sliver of undecided voters," and that the larger challenge for Democrats in Boston is to speak simultaneously to partisans and the undecided.

Reed's own party offered a case study of how not to do this, he said. Patrick J. Buchanan's divisive speech at the 1992 Republican convention in Houston created an impression of extremism that contributed to President George H.W. Bush's defeat by Clinton.

To exert more control over podium rhetoric four years later, Dole did not grant his nomination competitors speaking time.

Kerry will let this year's losing Democratic candidates speak, a campaign official said, though the times have not yet been announced and -- with the exception of Sen. John Edwards (N.C.), Kerry's vice presidential pick -- are unlikely to be in prominent places on the schedule.

There are few such places on the schedule. The major broadcast networks are planning only an hour of prime-time coverage on three of the four nights. They do not plan to break into regular programming on July 27.

If the GOP set the standard for a bad convention in 1992, Clinton and Democrats in New York that year set the standard for what can happen when things go well. He roared from third place in the polls -- behind independent Ross Perot -- to a leading position that he never surrendered.

Hollywood producer Harry Thomason, a Clinton friend who played prominent roles in staging the 1992 and 1996 conventions, said he sympathizes with Kerry's challenge.

"You're trying to create excitement and get people to pay attention to something the television networks regard as an archaic event that they shouldn't even be covering," he said. He added that he hopes Kerry has a few dramatic surprises in store, beyond the schedule announced yesterday. "For a lot of people, the only reason to watch conventions is to see what kind of razzle-dazzle they are going to have."

John F. Kerry's acceptance speech is set for July 29 and will be a crucial event for the Democrat.