WASHINGTON – Diesel fuel will average $2.27 a gallon this year and $2.54 in 2010, down substantially from previous projections, the Department of Energy said.

Trucking’s main fuel averaged $3.79 at the pump last year, DOE said in its monthly short-term energy outlook. Its December forecast projected the 2009 average would be $2.47 a gallon.

The national average diesel pump price in DOE’s weekly survey released Monday was $2.314, a 2.3-cent increase from last week that marked just the second uptick in the past six months.

DOE projected a continuing decline in diesel consumption in the United States and a slowing of distillate fuel use outside as factors in the projected price downturn.

Regular-grade gasoline is projected to average $1.87 this year and $2.18 a gallon in 2010, DOE said. The previous forecast put this year’s average at $2.03.

DOE weekly survey released Monday put the price at $1.784 — up a dime from last week and the second straight increase — but down substantially from the record $4.114 set in July.

Having fallen from record highs to below $40 per barrel, crude oil — which averaged $100 per barrel in 2008 — will average $43.25 this year and 2009 and $54.50 in 2010, DOE said.

Last month’s forecast put the price outlook for this year at $51 a barrel.