More than 46,000 people were killed and 3.4 million suffered injuries in motor vehicle crashes last year that cost Americans at least $74 billion, the Transportation Department has reported.

"These staggering dollar figures represent only a portion of the total cost of motor vehicle crashes," said National Highway Traffic Safety Administrator Diane Steed. "It is impossible to place a monetary value on the pain, suffering and loss of life."

Steed said about $60 billion of the economic loss could be saved if crashes, injuries and deaths were reduced.

"If we can continue to increase safety belt use, enforce posted speed limits and crack down on drunken driving, we can go a long way toward ending this drain on our financial resources, as well as preventing human tragedies," she said.

But consumer advocate Ralph Nader, who has been crusading for stronger auto safety, said he blames the Reagan administration for "not implementing the auto and highway programs that would reduce these human and economic costs."

"Specifically, they {Transportation Department officials} have dragged their feet on air bags, side-impact standards for light trucks and have not recalled many of the cars they should have."

The government estimated the economic cost of motor vehicle crashes at $27.37 billion for property losses, $20.86 billion for insurance expenses, $16.38 billion for productivity losses, $4.32 billion for legal and court costs, $4.12 billion for medical costs, $700 million for emergency costs, and $45 million for other costs.

Nine out of 10 accidents involved no personal injury, Steed said.