"That would not be possible. Everything depends on this time schedule," Smart head Ulrich Walker told Reuters on the sidelines of the North American International Auto Show.
Chief Executive Dieter Zetsche had also pushed for a quicker start, but Walker had to turn his boss down.
He cited the U.S. certification process, the delivery of engines from partner Mitsubishi Motors Corp. and the process of selecting 50 to 60 U.S. dealers from the 1,100 that have shown interest so far.
In a second step, the dealer network will expand to around 100 as Smart targets what it estimates to be a potential U.S. customer base of around 38 million "creative class" urbanites.
The world's fifth-biggest carmaker last year selected UnitedAuto Group as its exclusive U.S. distributor for the quirky two-seat car, which is already established in European markets.
A new version goes on sale in Europe in April and then in the U.S. market in the first quarter of 2008, where it will cost less than $15,000.
Walker declined to give a U.S. sales target for Smart. He said Smart would still make money on U.S. sales even if the euro stayed strong against the dollar.