EVANSVILLE, Ind. -- Just hours after his defeat in the Pennsylvania primary, Sen. Barack Obama took his campaign to Indiana, the next battleground in his primary election fight against Sen. Hillary Rodham Clinton.

"We won't just win in Indiana and the election in November, we will change this country. We will change the world," he said to a cheering crowd of about 7,000 at the indoor Roberts Municipal Stadium. "Let's get to work."

While some felt "we'd be blown out," the campaign worked hard and "closed the gap" in Pennsylvania, he said. He congratulated Mrs. Clinton and thanked the "hundreds of thousands of Pennsylvanians who stood with our campaign."

As they waited for Mr. Obama, the Indiana crowd cheered happily when early returns suggested a close race in Pennsylvania, then quieted a little while later when news organizations called it for Mrs. Clinton.

Sara Hess, 19, a freshman at the University of Southern Indiana registered to vote in her first presidential race, said the announcement had made her a little sad. She supports Mr. Obama, she said, in part because he "really wants to get the soldiers out of the war."

Mr. Obama's appearance was a sign of how quickly the race was moving on to Indiana, one of seven states and two territories, Guam and Puerto Rico, left to vote. Mrs. Clinton is favored in two states -- West Virginia and Kentucky -- while Mr. Obama is expected to take three -- North Carolina, Oregon and South Dakota. Indiana and Montana are the only states considered competitive.

The Illinois senator has a town hall meeting scheduled today in New Albany, another southern Indiana city, and Mrs. Clinton has an event planned in Indianapolis at midday and in Bloomington, Gary, East Chicago, Fort Wayne and South Bend later in the week.

With its primary late in the election season, Indiana, like Pennsylvania, is usually an afterthought in the process of nominating presidential candidates. And it is often ignored by candidates vying in the general election because it so reliably votes Republican.

But this year, both Pennsylvania and the Hoosier state have been put in the spotlight.

Mr. Obama has even suggested that the Indiana primary, with 72 delegates at stake, may be the "tiebreaker."

While some factors, such as an old industrial base and a large number of rural voters, would seem to favor Mrs. Clinton as they did in Pennsylvania, Mr. Obama is the senator from adjacent Illinois and has strong support in northwest Indiana.

That section of the state has a large share of black voters and is part of the Chicago media market, factors that help "level the playing field" between the two candidates in the Indiana primary, said Edward Feigenbaum, publisher of the Indiana Legislative Insight newsletter.

Polls are less clear on who might be ahead in the Indiana race than in the Pennsylvania primary, where Mrs. Clinton took an early lead that she never relinquished, even though the race tightened in the final weeks.

In Indiana, she also led early in most polls. One recent poll showed her ahead by 16 points, but two others each showed Mr. Obama leading by five percentage points.

Dr. Andrew Downs, director of the Mike Downs Center for Indiana Politics at Indiana University-Purdue University Fort Wayne, noted methodological differences in some of the polls. Still, the results suggest the gap between the two candidates is closing, he said.

Dr. Robert Dion, a political science professor at the University of Evansville, said the race is shaping up to be a "nail-biter."

"It'll be a very exciting and hard-fought stretch run," predicted Joe Hogsett, a co-chair for the Indiana Clinton campaign.

With the contest considered so close, both campaigns have poured resources into the state, with more expected in the next two weeks. Mrs. Clinton; her husband, former President Bill Clinton; their daughter Chelsea; and surrogates acting on their behalf already have made dozens of stops around the state.

Mr. Obama also has made several trips to Indiana and has already aired frequent campaign ads. Each campaign has opened more than 20 offices or volunteer centers in a state with about half the population of Pennsylvania.

Veteran political observers said nothing like it has happened in the state since 1968, when Sen. Robert Kennedy defeated Sen. Eugene McCarthy and Indiana Gov. Roger Branigin in the state's primary election.

"These are very heady times for Hoosiers," Mr. Hogsett said. "For 40 years, we've played only a minor role in selecting the presidential nominee of our party.

"It's time for our concerns to be heard."

Mr. Hogsett said Mrs. Clinton would try to turn the tide in her favor by continuing to address issues of concern to many Hoosiers, such as health care and job growth.

Kip Tew, a co-chair for the state's Obama campaign, noted that Mr. Obama continued to lead his opponent in pledged delegates and total votes.

"We'll continue to compete in every single state," he said.

A number of the state's leading Democrats have lined up for Mrs. Clinton, including Sen. Evan Bayh, a former two-term governor. A national co-chair for her campaign, he has been mentioned as a possible vice presidential running mate.

Not surprisingly, the Indiana secretary of state reported earlier this month that since the 2006 general election, the names of more than 332,000 Hoosiers have been added to the voter registration rolls, including more than 150,000 since the start of the year.

Unlike Pennsylvania's primary, which is limited to registered party members, Indiana's primary is open to anyone. Voters do not have to be a member of a particular party to vote in that party's primary. Dan Parker, the state Democratic chairman, has expressed concern that some Republicans might cross over to influence Democratic races, particularly lower on the ticket. But officials said they did not expect significant numbers of Republicans to do so.

In Indianapolis, signs of unusually intense political activity and interest were evident earlier this week even before the Pennsylvania results were in.

At Monument Circle, where a memorial to soldiers and sailors marks the city's center, a group of volunteers were waving "Honk for Hillary" signs.

Many drivers sounded their horns in apparent agreement, though one man yelled out "Obama" as he passed.

One volunteer, local resident Jewel Van Dalsen, said she decided to help with phone calls, canvassing and other activities because she liked Mrs. Clinton's positions on issues, particularly health care.

Ms. Dalsen, 48, said she's operated a cleaning business for six years and now has two part-time staff. She had health care coverage for her business initially, but said she dropped it early on because she could not afford it for herself or her employees. She currently has no coverage.

"Hillary's health care plan will cover every American," she said.

While Mr. Obama's plan is similar, it wouldn't require coverage for all adults, she noted.

At Butler University, where a student irritated a visiting Chelsea Clinton with a question earlier this year about her mother's reaction to the Monica Lewinsky affair, Josh Casey, chapter coordinator for Students for Barack Obama, called the level of student interest in the race "absolutely astonishing."

"Everybody has picked a side," he said, "and it's rare that I encounter anybody who says, 'I'm not going to vote.' "