The Guardian spots the signs:

The British foreign secretary, William Hague, said after the London conference today that it was not one of the subjects of discussion. He said the issue "was not raised at the conference... and is not part of any agreement today". 

But the US Secretary of State Hillary Clinton suggested that it would be legal to arm the rebels. She told a press conference at the Foreign Office: "It is our interpretation that [UN Security Council resolution] 1973 amended or overrode the absolute prohibition on arms to anyone in Libya, so that there could be a legitimate transfer of arms if a country should choose to do that." ...

The US ambassador to the UN refuses to rule out arming Libyan rebels. In an interview with ABC television, Susan Rice said: "We have not made that decision, but we've not certainly ruled that out."

Ackerman is keeping tabs on the "transatlantic tensions". Uri Friedman rounds up early opinions for and against the arming of rebels.