The same technological tools that have increased the nation's economic productivity have helped the United States become more energy efficient and may reduce emissions of greenhouse gases blamed for global warming, according to a report issued yesterday by the nonprofit Center for Energy and Climate Solutions.

In 1997 and 1998, the nation's economy grew by about 4 percent a year while the nation's energy consumption grew barely at all, the report said, suggesting that information technology and increasing use of the Internet are making the economy less dependent on energy.

The amount of energy required to produce a dollar of gross domestic product fell by more than 3 percent in 1997 and 1998, after declining by less than 1 percent a year in the previous 10 years, said principal author Joseph Romm, former assistant secretary in the Energy Department's Office of Energy Efficiency and Renewable Energy.

Romm is now executive director of the foundation-funded Center for Energy and Climate Solutions, which is working with the World Wildlife Fund to help businesses develop ways to reduce emissions of greenhouse gases.

"This is a very big deal if this is a trend and not an anomaly," he said, noting that it could result in revised energy, environmental and economic forecasts.

According to the study, at the same time that many businesses are making traditional improvements in energy efficiency, the Internet is also producing structural changes in the economy that may result in lower energy use, according to the report. Those changes include reducing the amount of floor space needed for retailing, replacing it with warehouses, which "typically use far less energy per square foot than a retail store."

The Internet might also reduce energy use in transportation as consumers substitute online shopping for trips to the mall, supermarkets and bookstores, the report speculates, although it suggests that the Internet's biggest potential for reducing energy consumption is in the industrial sector.

"If so, this would be the Internet's biggest impact on the environment, since this sector is responsible for a third of the nation's air pollution and the vast majority of its hazardous waste and other pollutants," said the report, which was coauthored by Art Rosenfeld, who founded the Center for Building Science at the Lawrence Berkeley National Laboratory, and Susan Herrman, an engineer and economist who works with Romm.

The report said its conclusions are only tentative because the Internet is growing so fast and because of incomplete data on it.

"I think we agree that there is not only a new economy but also a new energy economy," said Eileen Claussen, who heads the Pew Center on Global Climate Change. Claussen said that may result in reduced energy use and emissions, "but is it going to produce a free ride on reducing greenhouse gases, absolutely not," she said. "There's some cause for optimism, but not much more than that."