Former Iowa Gov. Tom Vilsack challenged a leading Democratic rival to a debate before union activists in Iowa later this month to talk about “central issues confronting America.”

But Barack Obama is not biting.

Vilsack is scheduled to participate in a Feb. 21 debate sponsored by the American Federation of State, County and Municipal Employees in Carson City, Nev. The Chicago Sun-Times reports that Obama opted to skip that debate, saying he’s committed to campaigning in Iowa that day.

Vilsack said he was willing to fly out immediately after the Nevada debate to attend a similar forum in Iowa.

“As you know, AFSCME represents workers throughout Iowa and they would be willing to organize a forum for us in any town on February 21,” Vilsack said in a letter to Obama’s campaign.

An Obama spokesman, said the senator would not participate in a February 21 debate with Vilsack or any of the other 2008 presidential candidates.

“Sen. Obama looks forward to participating in a number of debates during this campaign, but first he wants to personally meet with and hear from as many Iowans as possible about how we can change our politics,” Tommy Vietor said.

Obama has gotten heavy attention - most of it overwhelming praise - as he prepared to enter the contest for the Democratic presidential nomination over the past few months. More than 15,000 people showed up for his formal announcement in Springfield., Ill., on Saturday.

Vilsack left office last month and has struggled to get similar attention in his bid for the Democratic nomination. Despite being the first to throw his hat in the ring, he’s had a hard time garnering interest against the likes of Obama, Hillary Clinton or John Edwards.