An effort by the National Park Service to decrease noise from helicopters and small tour planes flying over the Grand Canyon has been thwarted by Congress.

Arizona Republicans and Nevada lawmakers of both parties worked together to craft legislation that effectively blocks a proposal by the park service to impose tougher noise standards on the US$120 million-a-year tour industry, which operates out of both states.

Their legislation was quietly inserted into a massive transportation bill that was passed by both the House and Senate on Friday and is expected to be signed into law by President Obama.

Environmentalists decried the action, saying it undermines a decades-long struggle to restore natural quiet to one of America's best-known and loved scenic wonders.

"This bill means that the Grand Canyon is going to stay noisy from air tours, and it's a good example of the effects of money on politics when you look at the stealth way that this was done," said Rob Smith, senior organizing manger for the Sierra Club in Phoenix. "The Grand Canyon is one of the 10 natural wonders of the world. It shouldn't sound like an airport."

But tour operators and their supporters in Congress said it stops government bureaucrats from imposing onerous regulation on an industry that provides 1,250 jobs in northern Arizona and the Las Vegas area. They say the industry already has invested millions in quiet technology aircraft.

"The Obama administration's misguided regulations were an unwarranted assault on an industry that was already taking precautions to protect the Grand Canyon experience for park visitors," said Rep. Paul Gosar, R-Ariz., who championed the bill in the House. "I am pleased to end the war on those rural Arizona jobs."

National Park Service officials in Arizona said they were still reviewing the bill Friday and had no immediate reaction.

The park service had been poised to release final noise regulations for the Grand Canyon air tour industry as early as July. The agency had issued a draft plan in February that would have required tour operators to achieve "substantial restoration of natural quiet" in the park by having no audible aircraft in 67 percent of the park from 75 percent to 100 percent of each day.

The bill passed by Congress says that the industry has to reach the goal of having no audible aircraft in 50 percent of the park at least 75 percent of each day. That standard essentially maintains the status quo, tour operators and environmentalists said.

It's not clear if the park service will go ahead and announce its final noise rule. But that rule would be superceded by the bill passed by Congress if it is signed into law by the president.

The bill requires the interior secretary to continue to monitor noise from the air tours to ensure compliance with the law. It also requires all commercial air tour aircraft operating in Grand Canyon National Park to fully convert to quiet technology within 15 years. Tour operators will be given incentives to convert their aircraft. Those incentives will include permission to operate more flights.

A spokesman for Papillon Grand Canyon Helicopters and Grand Canyon Scenic Airlines said the tour industry is committed to becoming quieter. But operators feared the reduced operating hours and route restrictions over Marble Canyon called for in the park service plan would severely damage business.

"It's a matter of fairness," said spokesman Alan Stephen. "The industry has risen up and done a tremendous amount to live with restrictions. The existing restrictions and our continuing conversion to quiet technology will improve the canyon dramatically. The restrictions the park service was proposing are unjustified."

But Rick Moore, director for conservation programs at the Grand Canyon Trust, said members of Congress and industry lobbyists have undermined years of effort by the park service to come up with a strong plan to restore natural quiet to the canyon.

"One of the reasons we have national parks is to provide people with an opportunity to experience quiet and solitude," Moore said. "We should be doing all we can in our national parks to provide that kind of experience. We're disappointed that Senators John McCain (R-Ariz.) and Harry Reid (D-Nev.) did this kind of end-run around the process."

McCain, in a joint statement with Sen. Jon Kyl, R-Ariz., said he believes the bill is a good compromise.

"This legislation thwarts a recent Obama administration proposal to ban up to 77 percent of the park from air tours, which would have killed hundreds of tourism jobs," the statement said. "That plan was deeply flawed and would have severely diminished a unique sightseeing experience. Fortunately, this provision ensures that visitors who might otherwise be unable to explore the Grand Canyon, particularly the elderly, disabled, and our nation's wounded warriors, will be able to continue to enjoy the canyon in one of the most unique ways possible."

About 70 percent of the the Grand Canyon visitors who take the helicopter and plane tours are foreign tourists who don't have a lot of time to spend in one place and want to get a quick bird's eye view of the canyon, Stephen said.