Traffic fatalities rose 3 percent over last year as Americans drove an estimated 1.7 trillion miles in 1984, National Highway Traffic Safety Administration officials said last week.

But more people would have died and the nation would have suffered greater economic loss had there been no programs to improve highway safety, the officials said.

A total of 43,862 people died on American roads this year, 3 percent more than the 42,584 killed in motor vehicle accidents in 1983, NHTSA officials said.

They said that increase largely is attributable to a rise in the number of vehicle-miles traveled, a figure used to indicate the number of miles traveled by all vehicles on U.S. streets and highways in a given year.

The 1.72 trillion vehicle miles traveled in 1984 was up from 1.64 trillion miles traveled in 1983.

By some estimates, the 1984 traffic-death toll translates to nearly $28 billion in lost productivity, increased insurance costs, medical and burial expenses and public assistance paid to survivors of crash victims.

When injuries, medical expenses and property damage are included in the calculations, the economic and societal cost this year of traffic accidents could rise to $100 billion, federally employed and privately funded highway-safety officials said.

The higher traffic deaths in 1984 raises questions about the effectiveness of federal, state, and local highway-safety programs, such as antidrunken-driving campaigns, the 55-mph speed limit, and multimillion-dollar seat-belt campaigns.

But NHTSA spokesman Richard Burdette and former NHTSA administrator Joan Claybrook, who heads a Washington-based product safety and consumer lobby, said those programs have helped limit the rise in traffic deaths at a time of increased highway travel.

"Because fatalities are going up, that doesn't mean the 55-mile-per-hour speed limit doesn't work. It means that even more people would have died in motor-vehicle accidents without the 55-mile-per-hour speed law," Burdette said.

Though the number of persons killed in vehicle crashes rose, the percentage of traffic fatalities for each 100 million vehicle-miles traveled has declined, NHTSA officials said. In 1973, when states began phasing in the 55 mph speed limit, there were 4.12 fatalities for each 100 million vehicle miles. There were 54,042 traffic fatalities that year for 1.3 trillion vehicle-miles traveled.

Claybrook said federal and private estimates indicate that 80,000 lives have been saved since 1968, largely because of rules designed to improve vehicle and highway safety. A January 1983 NHTSA report, "The Economic Costs to Society of Motor Vehicle Accidents," gives some idea of how much money the economy saved by sparing those lives, Claybrook said.

The report was based on figures compiled in 1980, a year in which there were 28 million accidents on U.S. roads involving 51,000 deaths, 4 million injuries, and property damage to 48 million vehicles. According to the report, the estimated cost of that human and mechanical destruction was $57.2 billion.

The costs generally were accounted for this way: $13.7 billion attributable to fatalities, $15.3 billion for injuries, $21.1 billion for property damage and $7.1 billion attributable to increased insurance costs for all drivers.