Gas-electric hybrid vehicles, the status symbol for the environmentally conscientious, are coming under attack from a constituency that doesn't drive: the blind.

Because hybrids make virtually no noise at slower speeds when they run solely on electric power, blind people say they pose a hazard to those who rely on their ears to determine whether it's safe to cross the street or walk through a parking lot.

"I'm used to being able to get sound cues from my environment and negotiate accordingly. I hadn't imagined there was anything I really wouldn't be able to hear," said Deborah Kent Stein, chairwoman of the National Federation of the Blind's Committee on Automotive and Pedestrian Safety. "We did a test, and I discovered, to my great dismay, that I couldn't hear it."

The tests — admittedly unscientific — involved people standing in parking lots or on sidewalks who were asked to signal when they heard several different hybrid models drive by.

"People were making comments like, 'When are they going to start the test?' And it would turn out that the vehicle had already done two or three laps around the parking lot," Stein said.

As gas prices continue to rise — along with concern about harmful emissions — hybrid cars are increasing in popularity. New hybrid vehicle registrations grew more than 49 percent nationwide in the first seven months of 2007 compared with the same period in 2006, according to R.L. Polk & Co., an automotive research firm. Toyota Motor Corp. has sold nearly 460,000 of the most popular hybrid model, the Prius, since it hit the market in 2000, according to the company, which pegs total hybrid sales at just over 900,000.

Officials with the Baltimore-based National Federation of the Blind are quick to point out that they're not advocating a return to gas guzzlers. They'd just like the fuel-efficient hybrids to make some noise.

NFB President Marc Maurer said he received an e-mail from an environmentalist who suggested that the members of his group should be the first to drown when sea levels rise from global warming.

"I don't want to pick that way of going, but I don't want to get run over by a quiet car, either," Maurer said.

The NFB — the leading advocacy group for 1.3 million legally blind people in the United States — made pleas to the auto industry and to federal and state agencies, with little concrete success so far. On Wednesday, the president of the NFB's Maryland chapter planned to present written testimony asking for a minimum sound standard for hybrids to be included in the state's emissions regulations.

But those regulations are crafted by the Maryland Department of the Environment, which has no oversight of auto safety, said Robert Ballinger, a spokesman for the department. He said the department would work with the NFB to press the issue with auto manufacturers and federal transportation officials.

Manufacturers are aware of the problem but have made no pledges yet. Toyota is studying the issue internally, said Bill Kwong, a spokesman for Toyota Motor Sales USA.

"One of the many benefits of the Prius, besides excellent fuel economy and low emissions, is quiet performance. Not only does it not pollute the air, it doesn't create noise pollution," Kwong said. "We are studying the issue and trying to find that delicate balance."

The Association of International Auto Manufacturers Inc., a trade group, is also studying the problem, along with a committee established by the Society of Automotive Engineers. The groups are considering "the possibility of setting a minimum noise level standard for hybrid vehicles," said Mike Camissa, the safety director for the manufacturers' association.

Officials with two separate arms of the U.S. Department of Transportation — the National Highway Traffic Safety Administration and the Federal Highway Administration — said they are aware of the problem but have not studied it.

While Stein said she would prefer that hybrids sound similar to conventional engines, other blind people said they'd be fine with any sound that was inoffensive but easy to detect. Both sides agree that it wouldn't be prohibitively expensive to outfit cars with an adequate noisemaking device.

"It's cheaper than an air bag or other safety devices," Kwong said. "Any kind of audio device is going to be relatively inexpensive."

The blind, however, will have to win over some hybrid owners as well as advocates for reduced noise pollution. Some think that making hybrids louder won't solve anything.

"To further expose millions of people to excessive noise pollution by making vehicles artificially loud is neither logical nor practical nor in the public interest," said Richard Tur, founder of NoiseOFF, a group that raises awareness of noise pollution.

Others believe that distracted pedestrians are at greater risk than blind people from quiet cars.

"The only way to function driving any car, forgetting the fact that it's a Prius, is to just be very careful and see who's around you," said George Margolin of Newport Beach, Calif., who runs a club for Prius owners with his wife. "We have to be as careful as anyone else and perhaps even more so."

Blind people are not the only ones who've had close calls. Linda Murphy, 57, a personal administrative assistant from San Marcos, Calif., has 20/20 vision when she wears her glasses, but she's almost been hit twice by hybrids.

"I'm walking right in back of it and it's moving and I didn't realize it until it nearly touched me," Murphy said, describing the first of her scares. "I never realized how dependent I was on my ears until I almost got hit."