CHICAGO — The third and final debate between Republican Alan Keyes and Democrat Barack Obama proved to be the most heated, as the two U.S. Senate contenders grappled with hot-button issues such as gay marriage and social policy.

Keyes and Obama expressed distinct differences on their views of government’s role in society during Tuesday’s debate at WTTW-TV studios on Chicago’s North Side.

Politicians should work with churches and community organizations to combat social ills, Keyes said, rather than creating a dependence on governmental intervention.

“These are things that have a moral dimension that cannot be addressed by bureaucrats and policy makers,” he said.

Obama countered Keyes’ argument with a stinging retort.

“When a child doesn’t have health insurance, he doesn’t need a lecture — he needs health insurance,” Obama said.

He said people with real problems need concrete help that the federal government can and should provide when preferable alternative solutions don’t exist at the local level.

Obama and Keyes traded barbs throughout the hour-long debate. Moderator Phil Ponce of WTTW-TV also struggled to maintain order, as the two candidates spoke over him during some of his attempts to change the subject. Ponce asked pointed questions that prompted Keyes and Obama to defend positions they expressed in previous debates and throughout their campaigns.

Obama hesitated as he tried to straddle the divide between preserving the traditional definition of marriage and allowing for civil unions that provide the same rights as marriage.

“We have a set of traditions in place that need to be preserved,” he said.

On the other hand, Obama said gays and lesbians “deserve the rights of citizenship” that include the transfer of property, tax equality and hospital visitation for gay partners.

Keyes found himself justifying his comments from last week’s debate about the connection between gay marriage and incest via artificial insemination. But Keyes stood his ground on the issue.

“If you can’t know who your sisters and brothers are,” he said, “there’s no way you could avoid having sexual relations with them.”

Although Keyes focused on clarifying his reasoning, Obama attacked the substance of the argument.

“Your logic wasn’t that complicated,” Obama said. “It’s just wrong.”

Gay marriage occupied a substantial amount of air-time during the debate and dominated all questions during the post-debate press conference.

The candidates agreed on few issues. Both said no new casino gambling should be allowed in the city of Chicago.

Twice during the debate, Ponce asked the candidates rapid-fire “yes” or “no” questions on domestic issues.

The candidates disagreed on drilling in the Alaskan National Wildlife Refuge, providing funding for research on additional stem cell lines and eliminating the electoral college. Keyes alone said “yes,” on the first issue, while Obama said “yes,” on the latter two.

On relations with Israel and global terrorism, the two candidates also differed sharply.

Keyes said the United States should not continue to broker peace agreements between Israeli and Palestinian leaders as long as the latter fail to put an end to terrorism.

“I think the real question is whether we ought to have said ‘no’ to terrorism years before we did and maybe even prevented the events of Sept. 11,” Keyes said. “The way to discourage terrorist activities is to make sure nobody benefits from terrorist activities.”

Obama remained firmly in support of the Middle East peace process, especially U.S.-led multilateral involvement in the process. The biggest problems in the war on terror, Obama countered, now are inadequate port inspections and security at chemical and nuclear plants.

“There are a whole host of domestic concerns that have been neglected by this administration,” Obama said.

Several issues came up during the press conference after the debate that neither candidate addressed earlier in the evening.

Illinois is “in a critical crisis situation” with the flu vaccine shortage, Keyes said. He supported Gov. Rod Blagojevich’s efforts to obtain FDA approval for the state’s purchase of extra vaccine doses from overseas.

“We must be willing to take extraordinary steps to meet extraordinary need,” Keyes said.

During the press conference, Obama also clarified his support for reforming the electoral college. He added that he would be in favor of a referendum in Illinois similar to one on the ballot in Colorado that would divide the state’s electoral college votes based on the percentage of ballots cast for each presidential candidate.

Both candidates said the debates provided an opportunity for voters to hear their positions.

Keyes called Tuesday’s debate a “vitally important demonstration for the people of the state of Illinois.”

“Both of us presented our views and they were tested,” Obama said.

Clinton J. Hubbell contributed to this report.

Reach Elaine Helm at [email protected].