The Obama administration said Wednesday it would push for a major shakeup in Syria's opposition leadership so that it better represents those dying on the front line, can rally wider support and resist attempts by extremists to hijack the revolution against the Assad regime.

Speaking to reporters in Croatia's capital, U.S. Secretary of State Hillary Rodham Clinton said the administration was suggesting names and organizations that should feature prominently in any new rebel leadership that emerges from talks starting next week in Doha, the capital of Qatar.

She dismissed the Syrian National Council, a Paris-based group of regime opponents who have lived in exile for decades, saying its leadership days are over, even if it could still play a role. The council was viewed with suspicion by rebels who stayed in Syria and fought the regime of President Bashar Assad.

"This cannot be an opposition represented by people who have many good attributes but have in many instances not been inside Syria for 20, 30 or 40 years," Clinton said. "There has to be a representation of those who are on the front lines fighting and dying today to obtain their freedom. And there needs to be an opposition leadership structure that is dedicated to representing and protecting all Syrians."

The shift in policy reflects as much the failure of the SNC to win widespread political legitimacy as the Obama administration's desire to be seen playing a leading role in shaping an opposition capable of winning the support of frightened Syrian minority groups and replacing Assad.

Republican presidential candidate Mitt Romney has criticized the Obama administration for spending too much time trying to win support for a Syrian political transition plan at the United Nations, where Russia and China have protected Assad from three damning resolutions. And he has called for stronger U.S. leadership in forging a cohesive body to lead Syria from decades of dictatorship.

The Obama administration insists it is already guiding such efforts, but Clinton's words appeared to demonstrate that it was stepping up its leadership role. She said the talks next week were sponsored by the Arab League but stressed that she has been constantly strategizing with European and Arab partners on the best path forward.

"We have recommended names and organizations that we believe should be included in any leadership structure," she said. "We've made it clear that the SNC can no longer be viewed as the visible leader of the opposition. They can be part of a larger opposition, but that opposition must include people from inside Syria and others who have a legitimate voice that needs to be heard. So our efforts are very focused on that."

At least 36,000 people have been killed in Syria since March 2011, according to activists. The last 19 months have seen the Assad regime's brutal crackdown on dissent descend into a full-scale civil war, with the resistance initially led by secular-minded opponents at least rhetorically committed to democracy. But as the violence has worsened, the rebels have increasingly come under the sway of Islamist and extremist influences.

Getting the political strategy right is key for the Obama administration because it has ruled out U.S. military assistance to the rebels or an American military intervention in the form of airstrikes or enforcing no-fly zone over Syria. It insists that it would be unhelpful to provide weapons to a questionable cast of rebel formations that may later use them against Israel or American interests.

Clinton said it was no secret that many in Syria, especially minority groups, are fearful about the prospects of Assad's government being replaced by the Sunni-led opposition. For the good of the country, she said, they must be assuaged.

"They have no love lost for the Assad regime but they worry, rightly so, about the future," she said. "So there needs to be an opposition that speaks to every segment and every geographic part of Syria."

She added: "We also need an opposition that will be on record strongly resisting the efforts by extremists to hijack the Syrian revolution. There are disturbing reports of extremists going into Syria and attempting to take over what has been a legitimate revolution against an oppressive regime for their own purposes."

Clinton also expressed her regret, but lack of surprise, at the failure of a proposed four-day holiday cease-fire in Syria. Despite the government's reported commitment, she said, it "did not suspend its use of advanced weaponry against the Syrian people for even one day."

"The shelling of the suburbs in Damascus was as bad last weekend as at any time in the conflict," Clinton said.

She said the U.S. would continue to support the diplomatic efforts led by U.N. peace envoy Lakhdar Brahimi to convince Moscow and Beijing to "change course and support a stronger U.N. action." But she said the U.S. cannot wait in the meantime.

"Instead, our efforts and those of our partners in the EU and Arab League are focused on pressuring the regime," Clinton said. A key plank is "helping the opposition unite behind a shared, effective strategy that can resist the regime's violence and being able to provide for a political transition that can demonstrate more clearly than has been possible up until now what the future holds for the Syrian people once the regime is gone."

In Paris on Wednesday, Russian Foreign Minister Sergey Lavrov underscored that his government wasn't changing its position, warning that the violence in Syria could spread terrorism throughout the Middle East and that ousting Assad's government would lead to more bloodshed.