DES MOINES, Iowa — Hillary Rodham Clinton will headline a high-profile fundraiser next month in the nation’s first Presidential caucus state of Iowa, creating a big campaign splash as Democrats scramble to hold a key Senate seat in November and the former secretary of state considers a campaign of her own in 2016.

Former President Bill Clinton and Mrs. Clinton will attend retiring Sen. Tom Harkin’s annual steak fry in Indianola on Sept. 14, Iowa Democrats said.

It will be the former First Lady’s first appearance in Iowa since 2008 when she finished a disappointing third in the state’s presidential caucuses.

Clinton has urged Democrats to mobilize for November’s mid-term elections and party officials said she would likely appear at other events around the country to help the party’s major fundraising committees.

And Harkin’s steak fry, an event that draws thousands of grassroots activists each year, and future presidential campaign staff and volunteers, could be among the biggest, potentially serving as the unofficial start of Clinton’s second Presidential bid. Early polls show her as the leading candidate to succeed President Barack Obama, her one-time rival.

Clinton is “looking forward to campaigning for her Democratic friends and colleagues and to helping the effort to move America forward,” her spokesman Nick Merrill said, adding that she’d “help raise money for important races in Iowa.”

Republicans need to win a net of six seats to take control of the Senate for the remainder of Obama’s term. The GOP is expected to maintain control of the House. Iowa’s Senate race pits Democrat Bruce Braley against Republican Joni Ernst in a campaign to succeed Harkin, who has held the seat for three decades.

Clinton has spent much of the summer promoting her book, Hard Choices, and stumbled when asked about her family’s post-Presidential wealth earned through six-figure speaking fees and other ventures.

Her return to the campaign trail on behalf of Democratic candidates has been widely anticipated as Obama’s approval ratings have sagged and some Democrats have sought to distance themselves from him in Republican-leaning states.

On a personal note, the Clintons’ daughter Chelsea is expecting her first child this fall and the former New York senator has said she does not want to make any political decisions before she welcomes her grandchild.

“If I decide to run, I will have a very specific agenda about what I think we should be doing,” Clinton said in an interview in July. She said the focus first should be on the midterm elections, however.

Democrats said Clinton’s fall campaign itinerary was still being formulated. She’ll appear alongside House Democratic leader Nancy Pelosi at a fundraiser in San Francisco in October to benefit female candidates.

Clinton, said Rep. Steve Israel, the Democratic Congressional Campaign Committee chairman, “is an extraordinary force for our values and will relentlessly fight to jumpstart the middle class.”

Iowa has had few visits from Democrats considering a 2016 Presidential run. Vice President Joe Biden headlined the Harkin steak fry last year and Maryland Gov. Martin O’Malley has made two trips to the state this summer, campaigning for local Democrats. Though Clinton has not returned to Iowa, the Ready for Hillary organization has been working on her behalf to sign up volunteers.

She last appeared at the steak fry in 2007 along with Obama and four other Democratic presidential candidates, an event that drew 15,000 Iowa activists.

The Aug. 24 cookout is considered a plum assignment for any Democrat considering a Presidential campaign. Clinton’s husband has appeared at the event three other times.

Organizers said the event at the balloon field would serve as a tribute to Harkin, who was first elected to Congress in 1974 and won his Senate seat a decade later.

Harkin, a liberal stalwart, has maintained close ties to the Clintons. He was among the field of candidates who competed for the 1992 Democratic presidential nomination eventually won by Mr. Clinton.

He said he was thrilled to welcome the Clintons to his final steak fry, noting that they were coming “as old friends and leaders of our party.”

Harkin said Clinton had not confided in him about her 2016 plans. “I’ll support Hillary for anything she wants to do. She’s that good a friend and that great a leader,” he said. “That’s a personal decision that she’s going have to make.”

In her recent book, Mrs. Clinton called the night of the 2008 Iowa caucuses “excruciating.” She finished behind Obama and 2004 Vice Presidential candidate John Edwards.

Bonnie Campbell, an Iowa chair of that Clinton campaign, said attending the steak fry in the battleground state would be a “win-win” for Clinton.

“I never heard her articulate anything negative about Iowa, quite the opposite,” Campbell said. Referencing a potential presidential campaign, she said Clinton will “be here because the process starts here. She’s a pragmatic person.”

(CATHERINE LUCEY and KEN THOMAS)