When President Clinton joins his wife for their first major joint campaign appearance today, the former president is planning to play the role of “biographer in chief,” telling “the story” of Senator Clinton — and directing some of his high-wattage charisma toward her.

But can the former president keep from stealing the show?

The extraordinary sight of the two Clintons on the stump in Iowa is expected to draw a press crush, dominating the holiday week news even as a handful of other presidential contenders campaign around the state. Clinton officials describe the former president’s participation as an obvious next step for the campaign, given that Iowa is the key primary battlefield where Mrs. Clinton, a Democrat of New York, is so far faring the worst.

The joint trip also brings challenges — and potential openings — for Mrs. Clinton’s rivals. Already, Senator Obama, a Democrat of Illinois, has questioned whether the former first lady can claim experience in the Oval Office based on her husband’s terms in office. Highly popular among Democratic loyalists, the former president has a tendency to overshadow his wife in public.

And, as always, introducing the good Mr. Clinton in public hazards reminding voters of the bad, particularly his affair with a White House intern and subsequent impeachment by the House nearly a decade ago.

Senator Clinton has concluded that the risk is worth the reward: She increasingly invokes her husband’s record and refers nostalgically to the 1990s in her speeches, citing his foundation work in statements about her own foreign policy agenda and referring to his presidency as the “last Clinton administration.”

Her husband is expected to take a somewhat different approach in the next week. Clinton advisers have scripted a role for the former president that focuses squarely on the candidate, not himself. During a handful of rallies — or, as they are being called, “Ready for Change, Ready to Lead” events — in Iowa, he is, advisers said, planning to walk listeners through his wife’s biography, particularly her work in children’s advocacy as first lady of Arkansas, on behalf of women as first lady, and as a senator for the past 6 1/2 years.

“He’s going to talk about her, and she’s going to talk about the country,” one Clinton official said.

“Nobody knows her better or longer than him, and we think he will do a great job in talking about her — her accomplishments, her record, her biography — as she lays out her vision for the country,” communications director Howard Wolfson said.

Clinton advisers do not, as a matter of course, discuss the downside to involving the former president, or even acknowledge the impeachment saga that consumed more than a year of his second term (except to note that the public continued to support him through the end of his administration and beyond). Even outside strategists say that there is good reason for Mrs. Clinton to use her husband as much as possible, particularly in the Democratic primary, given that the public will link them together, regardless of the role he plays.

“It’s always a smart strategy to lean into something” potentially difficult, said Chris Lehane, an adviser to former Vice President Gore, who avoided tying himself to Mr. Clinton during his presidential campaign in 2000 until the end.

“It’s not like you’re going to pretend the spouse isn’t the former leader of the free world. It’s smart to leverage it,” Mr. Lehane said. “And it’s much smarter, from a pure tactical standpoint, to deal with it earlier rather than later.” Referring to the current Clinton campaign, Mr. Lehane said, “Smart people over there have clearly thought about, ‘Does he introduce her? How does he introduce her?’ — all the things you would figure out to guarantee she continues to be the dominant figure in these events.”

At the same time, Clinton advisers believe that by focusing his introductions to comments about his wife, they can avoid awkward juxtapositions such as the joint appearance the Clintons made at the funeral of Coretta Scott King, the wife of the slain civil rights leader, where the senator was obscured by her dazzling husband. In a fund-raising pitch to supporters last week — with the subject heading “Having fun yet?” — Mr. Clinton gave a preview of how he will talk about his wife. He described her as “the best candidate to beat the Republican machine.”

“You know Hillary will never let a swift boat-style attack go unanswered,” he wrote. “When I met her more than 35 years ago, I thought Hillary had the best combination of mind and heart I’d ever seen — and I still do.”

The Clintons, who have mostly held fund-raisers together, will arrive in Des Moines tonight for a rally at the Iowa State Fairgrounds, anticipated as the biggest event of their three-day swing. They will drive east to Iowa City and Davenport the next day, winding up on the Fourth of July at a 40,000-person holiday parade in Clear Lake, followed by two more events that afternoon. Mr. Clinton will leave that day, with his wife continuing for a fourth straight day in Iowa on Thursday — a measure of how concerned the campaign is about her lackluster standing in the polls there.

So far, Chelsea Clinton, their only child, has played a much more limited role, attending occasional parties and fund-raisers but otherwise avoiding the campaign. Clinton advisers have said the couple wants to let their 27-year-old daughter, who now works for a hedge fund and lives in Manhattan, wait as long as possible before returning full time to the public glare.

But with the Clinton dynasty emerging at the center of the 2008 race, the other Democratic contenders are struggling with how to approach the former president; most campaigned for him in the 1990s, consider him a friend — and recognize his enduring star power within party ranks. Some advisers to rival candidates have predicted that Senator Clinton may suffer among women if she relies on her husband too much, but so far that does not appear to be the case.

During a campaign stop last week, Mr. Obama went the furthest of any contender in suggesting that Mrs. Clinton has less experience than she claims, a point that advisers to several Democratic candidates said they intend to keep raising.

“The only person who would probably be prepared to be president on Day 1 would be Bill Clinton — not Hillary Clinton,” Mr. Obama said at a fund-raiser in Chicago.

Mr. Obama’s comment was a shot at what is one of Clinton’s greatest strengths so far: Voters surveyed view her as the candidate in the race with the most substantial background. Starting this weekend, and continuing through the Iowa trip, Clinton campaign officials are working to build on that asset. The first campaign mailing — with the word “Ready” emblazoned across the front and more than seven times inside — is being mailed to Iowa caucus participants. It boils down her campaign platform (“Hillary believes America is ready for change” is one theme; “America is ready to end Bush’s war in Iraq” is another).

In a series of 12 photos, the mailing lays out her biography, from her days growing up in “a middle-class family in neighboring Illinois” to “working her way through law school.”

“As a mom, Hillary always made time for ballet recitals, shopping, and just spending time together,” says a caption under an old photograph of the senator and Chelsea. Further photos trace her traveling abroad as first lady; working on health care, and as a senator from New York. “Hillary Clinton — Ready to Lead,” the mailing concludes, asking whether voters are “ready to join.”