A new government study offers what could be a nightmare for Utahns on this tax-filing day.

Utahns - as well as residents of other Rocky Mountain states - who mail returns to the Ogden Internal Revenue Service Center may make more mistakes than people who send returns to the other nine centers nationally.But they don't get away with those mistakes because the center in Ogden is the most efficient at catching and correcting them.

That is according to information in a new study by the General Accounting Office, an investigative arm of Congress.

The study's aim was to show Congress how the IRS could better prevent and correct errors made by its employees. But information in it showed that residents of the mountain states make plenty of mistakes before the IRS ever touches their forms.

It showed that only 73 percent of the tax forms reviewed by the Ogden center's output review unit from March to September last year were received accurate from taxpayers - the lowest rate in the nation. The national average is 81.2 percent. The highest is 93.5 percent at the Austin, Texas, center.

The study noted that Ogden is the most efficient center in catching and correcting errors. While only 73 percent of returns were received accurate, 91.8 percent were correct by the time they left the center's output review.

That means 18.8 percent of all returns sent to Ogden's output review were in error but were corrected - the highest such percentage in the nation.Worse, Utahns are less able than residents of other regions to blame their mistakes on bad advice from the IRS.

The study said the Ogden center made fewer "critical errors" in its correspondence answering taxpayers' questions or in letters pointing out mistakes on returns.

For four of the seven months from February to August 1990, the Ogden center had the lowest such critical error rates in the country for mistakes reporting either the wrong information or not totally answering taxpayer questions.

For example, in February 1990 it had a 5 percent error rate - compared with a national average of 24.4 percent that month. In August 1990, its rate was 5.2 percent compared to a national average of 14.1 percent.

The study said the IRS nationally is making fewer mistakes in handling returns and in its advice on how to fill out forms.

It attributes that to "an increased emphasis on improving quality, the initiation of . . . quality reviews and a stabilizing work force of more experienced tax examiners."