The Port Authority has agreed to pay a California-based environmental consulting firm $8 million to conduct noise compatibility studies for Kennedy and LaGuardia airports and recommend ways to reduce unwanted sound.

Environmental Science Associates, based in San Francisco, will develop noise exposure maps to identify which neighborhoods surrounding the two airports are receiving excessive jet noise and come up with plans to mitigate its impact on residents, said officials at the bistate agency, which operates the airports in New York and New Jersey.

"It's been a long fight and now it's a reality," said Len Schaier, head of the Citizens for Quiet Skies over North Hempstead, one of numerous advocacy groups that have been working for years to cut aircraft noise over residential communities in Nassau County and Queens. "Finally, we're going to get data to help us understand how the changes to our airspace affect our environments," he said Tuesday.

The Port Authority is also hiring a consultant to conduct similar reviews at Newark Liberty International Airport and Teterboro Airport. Those proposals are due Nov. 10.

The studies at Kennedy and LaGuardia airports, expected to take three years to complete, must be approved by the Federal Aviation Administration.

The FAA, which sets noise standards for land use in and around the airports, measures noise by taking the average of all sounds emitted by planes in a 24-hour period, with greater weight given to aircraft noise between 10 p.m. and 7 a.m. This weighting reflects the added intrusiveness of night noise events. The measurement is called a day-night average noise level, or DNL, expressed in decibels.

Noise levels at DNL 65 dB or above are considered too high for residential neighborhoods and Congress has set aside money to help pay for noise mitigation projects that could include soundproofing homes.

Once the FAA approves the Kennedy and LaGuardia studies, the Port Authority could apply for federal money.

Kendall Lampkin, executive director of the Town-Village Aircraft Safety and Noise Abatement Committee, an umbrella organization that represents thousands of Nassau residents, said his group has been asking for these measurements, known as a Part 150 Noise Compatibility Study, for a decade and he is thrilled that is finally happening.

"I've waited 10 years to get one, and I can see light at the end of the tunnel," Lampkin said.

The Port Authority was ordered by Gov. Andrew M. Cuomo to conduct the studies early this year.

And, after much pressure from advocates and local officials, the authority has also agreed to expand the noise contour maps and look at communities impacted by aircraft noise at thresholds between DNL 55 dB and DNL 65 dB. This would likely include more neighborhoods in Nassau.

"DNL 55 dB is the standard used around the world, except the United States," Schaier said.