"Such a request was made" around the time of Israeli Prime Minister Benjamin Netanyahu's visit to Washington this week, the official said, confirming media reports.
But the official, who spoke on condition of anonymity given the sensitivity of the issue, played down as "unrealistic" reports that the United States would condition supplying the hardware on Israel promising not to attack Iran this year.
Netanyahu told Obama at a White House meeting on Monday that Israel had not yet decided on military action against Iran, sources close to the talks said.
Netanyahu has hinted that Israel could resort to force should Tehran - which denies suspicions that it is covertly trying to develop atomic bombs - continue to defy big powers' diplomatic pressure to curb its nuclear program.
The risk of an Israeli-Iranian war troubles President Barack Obama, who is up for re-election in November and has cautioned against kindling more Middle East upheaval. A Gulf conflict could send oil prices rocketing upwards.