BIRMINGHAM, Ala. (AP) - Newt Gingrich saw his presidential hopes all but dashed Tuesday in the Deep South, where he was rejected by voters in the very region that launched his storied political career more than three decades ago.

The former House speaker placed second behind rival Rick Santorum in primaries in Mississippi and Alabama after banking his candidacy on an all-Southern strategy that never fully bore fruit. Santorum's victories in states home to the Republican Party's most conservative voters all but ensures a head-to-head contest between front-runner Mitt Romney and the former Pennsylvania senator in upcoming contests.

Addressing supporters in a hotel ballroom in Birmingham, Ala., Gingrich said he was disappointed he had come up short but had no plans to leave the race. He fueled speculation that none of the candidates will have secured the delegates necessary to capture the nomination at the party's convention in Tampa, Fla., in August.

"When the primaries are over and it's clear no one person has won, who would do the best job of representing America and winning the election against Barack Obama?" Gingrich said to cheers.

Despite his defiant posture, the losses were devastating to Gingrich's candidacy.

He had campaigned hard across both states for nearly a week, stressing his connections to the Southeast and his understanding of the region's issues. He repeatedly mocked Romney's professed love of cheesy grits, saying he understood the Southern specialty far better than the Harvard-educated former Massachusetts governor who struggled to connect.

With gas prices rising, Gingrich focused his campaign appearances on energy policy and promoted increased oil and gas drilling - important industries in both Gulf Coast states. He delighted audiences by mocking Obama as "President Algae" for suggesting oil and gas could be developed from algae in the future.

But in the end, conservatives sided more with Santorum, a fiery social conservative whose values-laden message resonated with many voters.

Gingrich's biggest night of the primary season came in South Carolina in January, where his decisive 10-point victory over Romney re-energized his campaign after weak showings in Iowa and New Hampshire. His only other victory came last week in Georgia, which he represented in Congress for 20 years.

Gingrich planned to campaign Wednesday in Illinois ahead of that state's primary next Tuesday. He also was traveling Thursday to Louisiana, which holds its primary March 24. He told supporters to expect a three- or four-day period of questions about when he would leave the race. He also acknowledged he would face a challenge raising money.

Exit polls commissioned by The Associated Press and the television networks gave clues as to how Gingrich came up short.

Majorities in both states described his positions on the issues as about right, and he outpaced Romney in both states and Santorum in Mississippi as the candidate who best understands the problems of regular people. Gingrich's supporters were more strongly behind him than were voters backing Romney or Santorum, and he won among those voters who prioritized a candidate's experience.

But Gingrich faced competing challenges including single-digit showings among those seeking a candidate who had strong moral character. Gingrich has been married three times, and his messy personal history has been widely publicized.

He also suffered a sharp gender gap, and difficulty competing with Santorum for second place behind Romney among the less conservative slices of the electorate.