ARLINGTON, Va. - Newt Gingrich ended his run for U.S. president on Wednesday after dazzling in televised debates but slumping to defeat in dozens of Republican primaries under attack from rivals who portrayed him as the consummate Washington insider.

The former U.S. House of Representatives speaker, the face of the Republican Party in the mid-1990s, badly trailed front-runner Mitt Romney in polls and his campaign piled up a debt of $4.3 million.

Gingrich announced his departure from the White House race in a long statement to the media at a hotel in Arlington, Va., outside the capital that included references to his many grandiose ideas like the establishment of a U.S. colony on the moon.

He fell short of endorsing his former rival Romney but said voters had a clear choice in November's general election between Democratic President Barack Obama and the former Massachusetts governor.

"I am asked sometimes - is Mitt Romney conservative enough? And my answer is simple: compared to Barack Obama?" Gingrich said. "This is not a choice between Mitt Romney and Ronald Reagan. This is a choice between Mitt Romney and the most radical, leftist president in American history."

Gingrich, who had scaled back his campaigning for weeks after cutting staff, stood on a small stage with his wife Callista and other family by his side as he described his year-long presidential bid as "truly a wild ride."

"I could never have predicted either the low points or the high points. It was all sort of amazing and astonishing," Gingrich said.

He briefly led the Republican pack before the Iowa caucuses on Jan. 3 but fell victim to a new force in U.S. politics: the independent "Super PACs" or political action committees that have no limits on how much money they can raise or spend in support of candidates.

Although Gingrich had the support of one Super PAC, a pro-Romney group spent millions in negative ads attacking Gingrich, which was the start of his campaign's demise.

The former candidate must now work on paying off his debt. He was in talks with the Republican National Committee to figure out how to get some money. Romney's camp is not expected to directly help Gingrich pay it off but may introduce his team to donors who could help him in that effort.

"We have offered to be helpful," a Romney official said.

Awkward or attack dog?

Though Gingrich vowed he would work for the rest of this year to make sure his party wins the White House and Congress, some of his comments about Romney could come back to haunt him.

Obama's campaign wasted no time in producing a video splicing together sound bites of what it called "awkward moments" where Gingrich criticized Romney, called him a liar and questioned his fitness to serve as president.

Author of the Contract With America that helped Republicans win back control of Congress in 1994, Gingrich won primaries in South Carolina and his home state of Georgia this year but failed to make a mark in dozens of other states, including in larger ones such as Florida and Ohio.

Republican strategist Ford O'Connell said Gingrich will quickly be back on the campaign trail, likely as an "attack dog" for the Republican Party as it seeks to unseat Obama.

"The GOP needs him. They need conservative attack dogs who can break up the Obama message machine," said O'Connell. "He has the ability to take complex items and boil them down to be palatable Kool-Aid for conservatives."

"He's one of the best messengers of the right who, on a moment's notice, can rebut someone."

Gingrich's run turned ideas like establishing a U.S. moon colony and having school children work as janitors into front-page fodder. Last month he made headlines when a penguin bit his hand during a visit to a zoo in St. Louis.

Political commentator and former Gingrich adviser Matt Towery said the former presidential candidate would not have much gravitas talking about the economy on the Republican trail this year.

"Newt is of limited value now," said Towery of Gingrich, whom he has known for 32 years. "He has that massive debt, so it's hard to talk about fiscal issues."

His campaign was hurt by en masse staff desertions last year when staffers were fed up that Gingrich chose to take a Greek cruise with his wife instead of campaigning. Evangelicals are wary of thrice-wed Gingrich's marital history. He had an affair with Callista for years while married to his second wife.

He also faced criticism of being too much of a Washington insider as opponents publicized past lucrative contracts with mortgage giant Freddie Mac.

Romney issued a brief statement after Gingrich pulled out, saying that his former rival had brought "creativity and intellectual vitality" to American political life.

"During the course of this campaign, Newt demonstrated eloquence and fearlessness in advancing conservative ideas," Romney said in the statement. "I am confident that he will continue to make important contributions to our party and to the life of the nation."

Gingrich outlined a series of ideas he planned to pursue now that the campaign is over, and they sounded a lot like his regular campaign promises.

He said he wanted to talk about religious liberty, American energy independence, rain research and hopes to convince university students the importance of personal social security savings accounts.

The author of two dozen books, Gingrich is also likely to see his public speaking fees rise.