Three hours after renting a moped in Oak Bluffs Saturday morning, 30-year-old Katherine D. Miller tried to round a right curve on Beach Road near Harthaven, lost control of the moped and struck an oncoming car. She died of head injuries, becoming the fourth person killed in a moped accident on the Island since 1996.

"This was a horrific accident," said Dr. Alan Hirshberg, the director of emergency medical services at the Martha's Vineyard Hospital where the trauma team treated the victim. "She was extremely, critically injured with major injuries to the head and face."

Riding along on another moped with Mrs. Miller was her husband, Raleigh Miller, who witnessed the accident. The couple, from Alexandria, Va., were on the Island for the day and were apparently in the area to attend a wedding. They themselves had been married only 14 months ago.

The two were driving their mopeds toward Oak Bluffs shortly before 1 p.m., according to state police Sgt. Robert Moore. Witnesses saw Mrs. Miller lose control of her moped, her feet coming off the pedals just before she crossed the line into oncoming traffic. She collided with a 1988 Oldsmobile Delta 88 driven by Bethany Jeppsen, a 24-year-old from Alaska.

"She was launched from the moped and into the car windshield and landed on the pavement," said Sergeant Moore. He said there was nothing the driver of the car could do to avoid hitting Mrs. Miller. There is no shoulder, and wooden guard rails line the roadside of Beach Road along Farm Pond.

Mrs. Miller's moped was rented from The Lazy Pedaler, a business operated by DeBettencourt's Bike Shop on Circuit avenue extension, one of seven moped dealers in the town.

Last year, 66 moped riders ended up the emergency room being treated for accident injuries, according to a comprehensive survey started by Dr. Hirshberg.

This weekend's fatal accident comes just a few months after moped dealers agreed to implement a nine-point plan aimed at reducing the number of moped accidents. In exchange, moped opponents backed off proposed legislation that would require moped renters to have a motorcycle license.

Now, that deal appears to be in jeopardy. Sam Feldman, the founder of the Mopeds Are Dangerous committee, said yesterday he's not sure all moped dealers can be trusted to regulate themselves, to spend more time training renters and to hand out forms that spell out the risks of mopeds.

"A few of the dealers are responsible, but I watched last Tuesday to see who was giving out the inherent risk forms, and only half the shops are doing it," said Mr. Feldman. "They have to bear responsibility for the deaths and accidents of their renters. Unless they can self-regulate, we're going to go back to the legislature."

West Tisbury police chief Beth Toomey, who helped broker the agreement with moped dealers through a series of meetings, said yesterday she plans to sit down today with stakeholders - town officials, Dr. Hirshberg, moped dealers and members of Mr. Feldman's group.

"I'm very adamant that this is not an us against them situation. I don't want to lump all moped dealers into one bin," she said. "I stop moped riders all the time and ask them questions. Some dealers are very comprehensive about what they tell them. Other dealers are not."

The goal, she said, is to get them all doing the same thing. But it remains to be seen if coexistence can be achieved.

Oak Bluffs police chief Joseph Carter yesterday called mopeds unsafe, especially in the hands of people who lack experience riding a two-wheeled vehicle. "My suggestion is we either ban them or there should be an initiative to require they only be rented by people who possess a motorcycle license," he said.

While Chief Carter said he has not noticed any increase in the number of mopeds this year, one moped dealer, Fran Alarie 3rd, yesterday said that dealers, especially in Oak Bluffs, are renting many more mopeds to meet the demand of daytrippers coming off the cruise ships. On Fridays, close to thousand cruise passengers come ashore for the afternoon in Oak Bluffs.

Dr. Hirshberg has not finished tabulating up-to-date numbers for this year's survey of moped and bicycle accidents, but Mr. Alarie claimed that hospital officials told him the number of moped accidents has dropped slightly this year compared to figures last year.

Mr. Alarie has helped lead the other moped dealers to the negotiating table. He said people need to take into account the rate of accidents compared to the number of mopeds rented. Some 30,000 mopeds were rented on the Island in last year, he said.

The weekend's fatality, he hopes, will not ruin the efforts of both sides to keep working on the nine-point plan which includes a training video, new road signs and a special decal warning riders of risks.

"I'm not saying there won't be another fatality," said Mr. Alarie, "but if everybody stops talking, it won't solve anything." Dealers and their opponents need more time to sit down and talk, and more time to improve their operations, he said.

"I just took 17 people off mopeds this week," he said. "That would have been $1,000 to me, but they couldn't understand the concept of a throttle and brake."

Tonight, Oak Bluffs selectmen are expected to raise the issue of mopeds with leaders in search of ideas that would prevent more accidents. Selectman Richard Combra said his board would like to see dealers take more time training renters, but the problem is that they have almost no space for the training.

Yesterday morning at DeBettencourt's, four people were getting ready to rent two mopeds. The drivers did a quick lap around the parking lot by the harbor and then pulled back in to pick up their passengers. The employee, who asked not to be named, told the renters, "I don't know if you guys heard but someone just got killed riding a moped. If you feel at all uncomfortable, come back and we'll set you up with something else. There are buses here you can take and Jeeps you can rent."

As the renters sped off, the employee confided that this was his first summer on the Island, and he had no idea traffic here was so bad. "If I came here as a tourist," he said, "I'd take a bus."