Assistance could mean combat armor, vehicles and other equipment not deemed to be offensive, the officials said. It could include training in battlefield medical care and the protection of human rights, they said.
For now, the Obama administration is advancing more modestly. It is nearing a decision whether to give ready-made meals and medical supplies to the opposition fighters, who have not received direct U.S. assistance.
U.S. Secretary of State John Kerry was expected to announce the new contributions at the Rome conference, in addition to tens of millions of dollars intended for rule of law and governance programs.
The shifts in strategy are part of a step-by-step process that could lead to direct military aid to carefully screened members of the Free Syrian Army if the nearly 2-year conflict continues. Some 70,000 people have died in the fighting.
The European Union last week renewed an arms embargo against Syria for three months. But foreign ministers made clear that the decision could be reviewed while they look at ways to increase pressure on Assad to leave.
Washington has provided $385 million in humanitarian aid to Syria's war-weary population and $54 million in communications equipment, medical supplies and other nonlethal assistance to Syria's political opposition. The U.S. also has screen rebel groups for Turkey and American allies in the Arab world that have armed rebel fighters.
No U.S. dollars or provisions have gone directly to rebels. That decision reflects concerns about forces that have allied themselves with more radical Islamic elements since Assad's initial crackdown on peaceful protesters in March 2011.
Kerry said Wednesday in Paris that both the U.S. and Europe want a negotiated solution to the crisis and would speak to the leaders of the Syrian National Coalition about that. He also said the world must be prepared to do more to support the rebels and he accused Assad's government of engaging in "criminal behavior."
"We want their advice on how we can accelerate the prospects of a political solution because that is what we believe is the best path to peace, the best way to protect the interests of the Syrian people, the best way to end the killing and the violence," he said at a news conference with French Foreign Minister Laurent Fabius.
"That may require us to change President Assad's current calculation," Kerry said. "He needs to know that he can't shoot his way out of this. And so we need to convince him of that, and I think the opposition needs more help in order to be able to do that."
Fabius offered a similar assessment.
"The situation is unbearable and we need to find the means to a transition and for Assad's departure," he said. "We agree all of us on the fact that Mr. Bashar Assad has to quit."
Britain's Foreign Office also said it would increase its support for Syria's opposition.
The possibility of a sudden change in U.S. strategy comes as President Barack Obama begins a second term and Kerry succeeds Hillary Rodham Clinton as the top U.S. diplomat.
Freed from the constraints of a re-election campaign, administration officials say there is greater leeway now for new approaches than last year, when Obama rebuffed a plan by Clinton, then-CIA Director David Petraeus and then-Defense Secretary Leon Panetta to arm the Syrian rebels.
The administration remains cautious, officials say, and is resisting European pressure to expand military aid to include the kind of items that Britain and France are considering.
Few Americans want to see their country dragged into another war of complicated loyalties and sectarian rivalries in the Muslim world, a little more than a year after leaving Iraq and with 66,000 U.S. combat troops still in Afghanistan.
Administration officials say they don't have enough assurances that rebel units under the sway of Islamic fundamentalists won't turn their weapons on Israel or other U.S. allies and fragile states in the region.
Lebanon is torn by some of the same internal sectarian divisions as Syria and Jordan is struggling with its political reform path.
Iraq's prime minister, Nouri al-Maliki, warned on Wednesday that a victory by Syrian rebels would lead to more fighting in Iraq and a new haven for al-Qaida.
Greater instability in any of Syria's neighbors would pose a whole new set of problems.
Still, officials said the U.S. was considering a gradually upgraded involvement in Syria to bolster moderate forces within the rebel ranks and help the fledgling political opposition win greater backing among Syrians, especially minority groups that have remained largely loyal to Assad and his government.
Debate within the administration on how best to accomplish these goals has increased in recent months as diplomatic efforts have failed to end the war. The Syrian opposition insists that only weapons, intelligence support and other forms of military aid truly can tip the balance.
U.S. Sen. Marco Rubio, a potential 2016 presidential candidate, urged the administration to consider lethal aid.
"We should want the best organized, the best equipped and most dominant groups in the opposition to be groups that are friendlier to our national interests," Rubio, a Florida Republican, said Wednesday at the Washington Institute for Near East Policy.
The position is similar to one Kerry held as a senator, and one he reminded reporters of this week when he proposed the creation of opposition safe zones and suggested providing rebels with U.S. weaponry.
But in his first month as secretary of state and on his first official trip overseas, the 2004 presidential candidate has been vaguer.
"We have a lot of ideas on the table, and some of them, I am confident, will come to maturity by time we meet in Rome," Kerry said this week. "Others may take a little more of a gestation period, but they're no less part of the mix and part of the discussion.
"What I can tell you is we are determined that the Syrian opposition is not going to be dangling in the wind wondering where the support is or if it's coming, and we are determined to change the calculation on the ground for President Assad."