"This presidential race is over for me," Santorum told reporters in Gettysburg, in his home state of Pennsylvania.
Despite an upset victory in the first Republican nominating contest in Iowa in January that led to a surprising showing with victories in 10 more states, Santorum failed to build sufficient momentum to derail frontrunner Romney.
He trailed a distant second in the battle to be the party's contender aiming to thwart Obama's hopes of a second term, outspent by Romney's deep war chest and out-organized by an extensive grassroots network.
Last weekend, the former Pennsylvania senator halted campaigning for four days after his youngest daughter, Bella, who suffers from a rare genetic disorder, was hospitalized again.
Santorum acknowledged it had been a "difficult weekend," and said while Bella was getting better, "it did cause us to think."
"While this presidential race is over for me and we will suspend our campaign effective today, we are not done fighting," he said as he pledged to do what he can to help defeat the Democratic incumbent in November.
"We're going to continue to fight for the Americans who stood up and gave us that air under our wings that allowed us to accomplish things that no political expert would have ever expected."
In his speech, Santorum did not once mention Romney, who will clearly need Santorum's backing if he is to corral the support of evangelical Christians and core conservative voters.
But Santorum spokeswoman Alice Stewart told CNN the pair had a "nice conversation" earlier today, and would have "another conversation in the next few days and weeks."
The two have "great mutual respect for each other," she said, while acknowledging that "politically, they disagree on some of the key issues."
Santorum quit the race just two weeks before a primary vote in Pennsylvania, amid polls showing he could lose the state to Romney.
Santorum had already suffered a massive home defeat in 2006, when he was bounced out of the US Senate by a Democratic challenger, and losing in Pennsylvania a second time would be a disaster for the political brand of a man many experts have said could be laying the groundwork for another run in 2016.
With Romney enjoying a commanding lead in the delegates race that determines the nominee, the Republican establishment had been urging Santorum to step aside and allow the party to coalesce around a single candidate.
Romney swiftly congratulated Santorum for being "an able and worthy competitor" and for the campaign he had run.
"He has proven himself to be an important voice in our party and in the nation," Romney added.
The Republican National Committee called Santorum's decision to drop out "commendable."
Obama's campaign manager Jim Messina meanwhile used the opportunity to take aim at Romney, saying: "It's no surprise that Mitt Romney finally was able to grind down his opponents under an avalanche of negative ads."
A devout Roman Catholic, Santorum's far-right views on religion, women and marriage played well with the conservative base, but were alienating the all-important voting bloc of moderates and independents.
The 53-year-old was a virtual unknown nationally when he first threw his hat into the Republican ring in June.
Despite being written off early, Santorum had improbable successes in the US South and Midwest.
"It was a love affair for me going from state to state," he said Tuesday.
His pro-life, anti-contraception, anti-gay-marriage message gained traction with heartland evangelicals deeply skeptical of Romney, who they view as a moderate disguised in conservative clothing.
Romney, the millionaire ex-governor of liberal leaning Massachusetts, has also stirred controversy, with many saying he is out of touch with ordinary people struggling in the tough economy.
And Santorum was criticized for dwelling on contentious social issues at a time of economic hardship.
Pressure will now build on former House speaker Newt Gingrich to drop out and let the party coalesce around Romney.
But Gingrich insisted he will take his campaign to August's Republican national convention despite little to no chance of winning enough delegates.
"I am committed to staying in this race all the way to Tampa so that the conservative movement has a real choice," said Gingrich, who wasted no time in urging Santorum supporters to "join us."
Gingrich, who has won two contests, acknowledged Sunday that Romney was his party's "most likely" nominee and pledged to support him if Romney gets the 1,144 delegates to clinch the nomination.
Libertarian Texas congressman Ron Paul also issued a statement saying he planned to "continue running hard" until the party convention in Tampa. (AP)
<관련 한글 기사>
美공화 샌토럼, 경선포기..롬니 독주체제
미국 공화당 대선주자인 릭 샌토럼 전 상원 의원이 10일(현지시간) 경선 중도포기를 전격 선언했다.
샌토럼 전 의원은 이날 자신의 `정치적 고향'인 펜실베이니아주(州) 게티스버그 에서 기자회견을 통해 "나의 대선레이스는 이제 끝났고, 우리는 오늘부터 선거운동을 중단할 것"이라고 말했다.
그는 "그러나 싸움이 끝난 것은 아니다"면서 오는 11월 6일 본선에서 공화당이 버락 오바마 미국 대통령을 이길 수 있도록 계속 노력하겠다고 밝혔다.
그는 특히 "온갖 어려움에도 불구하고 우리는 11개 주에서 승리를 일궈냈고, 수백만표를 얻었다"면서 "밋 롬니(전 매사추세츠 주지사)가 더 많은 대의원을 확보했지만 우리는 다른 방식으로 이겼고 우리는 보수적인 메시지로 유권자들을 마음을 움 직였다"고 강조했다.
샌토럼 전 의원은 공화당 대선후보 선출을 위한 첫 경선전인 아이오와 코커스(당원대회) 승리를 시작으로, 당 안팎의 예상을 깨고 초반 `돌풍'을 일으키며 롬니 전 주지사와 양강 구도를 형성해 왔다.
특히 그는 자금ㆍ조직력 열세에도 불구하고 `발로 뛰는' 선거운동을 통해 바닥표를 훑으며 선전했으며, 중도성향이 강한 롬니 전 주지사에 맞서 보수층을 겨냥한 전략으로 일각에서 `보수 대표주자'라는 평가도 받았다.
그러나 공화당 전당대회에 참석하는 대의원 확보 경쟁에서 롬니 전 주지사에게 크게 뒤진데다 오는 24일로 예정된 펜실베이니아주 프라이머리(예비선거)에서도 패색이 짙어지면서 포기를 선언했다.
이날 CNN방송 집계에 따르면 샌토럼 전 의원이 지금까지 확보한 대의원 수는 27 5명으로 롬니 전 주지사(651명)의 절반에도 못 미쳤다.
아울러 '3염색체성 18(trisomy 18)'이라는 선천성 장애를 앓고 있는 막내딸 이사벨라의 건강 문제도 중도포기의 요인이 된 것으로 알려졌다. 이날 기자회견에는 그의 가족도 자리를 함께 했다.
이날 샌토럼 전 의원이 `중도 포기'를 선언함에 따라 올 연말 본선에서 버락 오 바마 대통령과 승부를 겨룰 공화당 대선주자는 사실상 롬니 전 주지사로 확정됐다고 전문가들은 분석했다.
롬니 전 주지사는 이날 성명을 내고 "샌토럼 전 의원은 능력있고 훌륭한 경쟁자 "라면서 "그는 우리 당과 이 나라에서 중요한 목소리를 내고 있음을 입증했다"고 치 켜세웠다.
샌토럼 전 의원은 롬니 전 주지사와 사퇴 문제를 논의한 것으로 알려졌으나, 이 날 기자회견에서 지지 의사를 밝히지는 않았다.
대선주자인 뉴트 깅리치 전 하원의장은 지난 8일 폭스뉴스에 출연, "롬니 전 주 지사가 대의원 수의 절반을 확보한다면 그를 지지할 것"이라면서도 본선까지 완주하겠다는 입장을 밝혔다. (연합뉴스)
