WASHINGTON — The average fuel efficiency of U.S. cars and trucks sold in the 2006 model year showed no improvement from the year before at 25.4 miles per gallon, as increased sales of fuel-thirsty cars offset slightly more efficient trucks, according to federal data.

The figures — the first new data in two years — will likely add to the push in Washington for higher efficiency standards. Several lawmakers want to require U.S. automakers to meet steep annual increases in fuel economy rules.

President Bush has said he favors a goal of 4 percent annual increases through 2017, but has declined so far to back requiring the increases, and automakers have called such hikes unrealistic.

"If we're yet again stuck in neutral despite gas prices hitting $3 a gallon, it sends a clear message to me that Congress and the president need to pass higher fuel-economy standards for the fleet," said David Friedman, research director of the Clean Vehicles Program at the Union of Concerned Scientists.

Detroit automakers turned in a mixed performance, with flat to lower results for cars and only DaimlerChrysler AG posting a gain in truck efficiency. Toyota Motor Co. and Nissan Motor Co. raised their averages for their North American-built cars and trucks, while Honda Motor Co.'s figures held steady in cars but fell for trucks.

The report by the National Highway Traffic Safety Administration estimates automakers' progress toward meeting the standards set by the Corporate Average Fuel Economy program of 27.5 mpg for passenger cars and 21.6 mpg for pickups, vans and SUVs.

Based on estimates from midmodel year sales, the report said automakers were on track to average 25.4 mpg across all vehicles sold, the same as in the 2005 model year. While the fuel efficiency of trucks was forecast to rise by 0.1 mpg to 22.2, passenger car fuel economy was expected to fall by half-a-mile per gallon to 29.8.

The final figures, based on sales totals, could move slightly up or down.

GM's domestic car fleet averaged 29.2 mpg, the same as a year earlier, while its truck fleet fell 0.1 to 21.7 mpg Ford Motor Co.'s averages declined for both cars and trucks, with a 0.4-mpg drop in cars to 28.2 and a 0.6-mpg drop in trucks to 21.1.

Ford spokesman Mike Moran said production changes and mix shifts, such as declining sales of the small Ranger pickup, contributed to the company's fuel-economy declines. With increased sales of more efficient new models such as the Ford Fusion, "we believe we'll see something more to the positive in the next round," he said.

DaimlerChrysler's trucks also averaged 21.7 mpg, an increase of 0.4 from 2005, but its domestic car fleet fell to 25.7 mpg, from 28.8 mpg, the largest decrease among the top six automakers.

With sales of vehicles such as V8-powered models of the Chrysler 300 sedan, DaimlerChrysler was the only full-line automaker to fall short of the fuel-economy standard for passenger cars.

Spokesman Colin McBean also said the company's results suffered from the wind-down of production on several of its older small cars, such as the Neon and Stratus, before newer models such as the Dodge Caliber and Jeep Compass ramped up.

Automakers can miss the CAFE targets in a model year if they have accumulated credits from surpassing the standards in earlier years, or tell NHTSA how they plan to make up the shortfall in future model years.

As in prior years, the largest Japanese automakers posted higher fuel-economy averages, thanks to the popularity of their smaller vehicles.

Toyota had the most fuel-efficient North American-built cars of any automaker, averaging 34.7 mpg, an increase of 0.3 from 2005. Its trucks averaged 23.6 mpg, up from 23.1 mpg a year earlier.

Honda's domestic car average was flat at 33.2 mpg, while its truck fuel efficiency declined by 0.4 mpg to 24.5. Nissan increased its car and truck averages, to 30.9 mpg for cars and 21.9 mpg for trucks.