BILLINGS (AP) -- Motorcycle deaths are approaching a 20-year high in Montana this year, a trend that could reflect an upswing in their popularity in recent years.

Through the second week of Sept. 26 motorcycle riders have been killed in wrecks throughout the state. That is a 37 percent increase over the 18 deaths reported during that same period last year, and the highest number of deaths since 34 motorcyclists were killed in 1985, the state Department of Transportation's Highway Traffic Safety Office said.

Jack Williams, an operations research analyst for the safety office, said the rising death toll is likely the product of having more riders on the road.

''It's not like motorcycles are suddenly unsafe," he said. ''It's a function of the number of motorcycles more than anything else."

Between 1997 and 2004, motorcycle registrations in Montana nearly doubled, increasing from 17,978 to 34,433. The total number of wrecks involving riders rose from 307 in 1997, to 400 in 2004.

Williams said registrations are expected to top 40,000 by the end of the year, likely boosted by high gas prices and retirees returning to an old hobby.

Nationwide, motorcycle rider deaths increased for the seventh year in a row, even as deaths involving other motor vehicles dropped for the second year in a row, an annual study by the National Traffic Safety Administration shows.

Montana, Williams said, could see more fatalities as the number of motorcycle riders here continues to surge.

''Statistically, fatalities bounce around humongously from year to year," he said. ''You really have to look at long-term trends. I keep thinking the number is going to take off and we're going to have 40 fatalities one of these years, but it hasn't happened.

A mandatory helmet law could help reduce fatalities, authorities said. They blame many fatal motorcycle wrecks on lack of experience among first-time and returning riders.

Col. Paul Grimstad, head of the Montana Highway Patrol, said young riders take to high-performance sport bikes with little exposure to riding, while ''50-something riders" purchase Harley-Davidson bikes and often find themselves ill-equipped to handle their power.

''That seems to be the consensus about a lot of these (deaths)," he said.

Although the rising fatality levels are a concern, Highway Patrol officers say they continue to rely on traditional means to try to curb rider deaths, focusing on keeping troopers visible to help reduce speed and recklessness among motorcyclists, Grimstad said.

The state also helps support a motorcycle safety program to help combat inexperience.