WASHINGTON - The government is banning Jet Skis and their ilk at scores of national parks and seashores but letting them roar on in the parks where they're used most, including at Lake Mead in Arizona and Nevada.
''Personal motorized watercraft,'' widely known by the trade name Jet Skis, are said by critics to shatter the tranquility of many parks and pollute the air and water. Enthusiasts say the machines are quieter and cleaner than in the past.
In issuing regulations that take effect April 20, the National Park Service acknowledged Tuesday it was trying to pursue a middle path.
Robert Stanton, the agency's director, called the new restrictions ''a prudent approach'' that will allow some use of the watercraft ''yet protects park values ... and reduces conflicts with park visitors who seek solitude and traditional recreational activities.''
Under the Park Service regulation, Jet Skis will be banned in 66 parks, recreational areas and seashores, although in many of those areas the craft have not been used widely.
At the same time, the agency said Jet Skis, and similar personal motorized watercraft, may continue to be used at 10 federal recreational areas where water sports traditionally have been a focus of activity.
And it gave 11 other park areas - mostly federal seashores - a two-year ''grace period'' before they have to eliminate Jet Ski use, or obtain a special approval.
Environmental groups accused the Park Service of caving in to pressure from the watercraft's users. The industry estimates there are 1.2 million Jet Skis or similar watercraft in use.
''The Park Service has admitted that Jet Skis pollute the air and water, harass wildlife, and interfere with other visitors. Yet they still propose to allow most use to continue,'' complained Tom Kiernan, president of the National Parks and Conservation Association, a private park advocacy group.
But the Personal Watercraft Industry Association wasn't happy about the rule either.
Larry Lambrose, the association's executive director, said the ban was too broad and that even at the places given the two-year grace period, local park officials could impose a ban. He disputed that the craft pose environmental or safety problems and said in newer models, noise and pollution have been reduced significantly.
The agency said the Jet Skis could continue to be used indefinitely in the 10 national recreational areas because ''water-related recreation was a primary purpose'' when they were created.
These included Glen Canyon along the Arizona-Utah line, where tens of thousands of boaters go for water recreation, and Lake Mead in Arizona and Nevada.
In all, the Park Service considered 87 parks, recreational areas and seashores where motorized boating is allowed. While Jet Ski use is marginal in many of these parks, in 32 of the areas use of Jet Skis has increased dramatically in recent years, the Park Service said.
In 66 of the 87 areas, local superintendents will have to get approval from Washington, in a formal rule-making, if Jet Skis are to be allowed, the agency said. In the 11 cases given the grace period, superintendents will have to get approval, on a case by case basis, if the watercraft are to be used beyond the two years.