"The main problem is technical ... and this problem will take time ... a year or 15 months," Bremer told a pan-Arab satellite channel in an interview on Saturday.
Bremer noted the absence in Iraq of voter lists or legislation covering elections and political parties as, he said, a visiting UN team highlighted last week.
"These are major technical difficulties which are an obstacle to elections and make it impossible," to hold them.
Shia, who contest US plans to hand power over to an unelected authority in the summer, have demanded to know when national polls will finally be held after UN Secretary General Kofi Annan recommended on Thursday that elections be put off and a caretaker regime selected for the short term.
Also on Saturday, an Iraqi was killed and a US soldier wounded when gunmen ambushed three American civilian cars in Haswa, 30kms southwest of Baghdad, the US military said.
The attackers opened fire from a car, shooting dead an Iraqi translator and wounding a US soldier, a US military official said.
American troops had been travelling in the unmarked Ford Explorer vehicles when the attack happened.
"There was a shoot-out. We found a dead Iraqi interpreter with a US government ID," he said, adding that a 9mm handgun was found at the scene.
In the hail of gunfire, one of the cars burst into flames, coming to a standstill a kilometre down the road. A second crashed in the middle of the road, while the third escaped unscathed, said witnesses.
US forces quickly cordoned off the scene of the attack in an
area that has been blighted by persistent shoot-outs.