WASHINGTON — The Federal Trade Commission said it would accelerate a review of its decade-old "green" marketing guidelines because of the booming number of businesses that are persuading customers to purchase certificates or pay premiums to help pay for projects or practices that purportedly benefit the environment.

The FTC, which was scheduled to review its guidelines in 2009, said that on Jan. 8, in the first of a series of public meetings, it would examine carbon offsets and renewable energy certificates that claim to reduce greenhouse gas emissions in one place to offset emissions elsewhere.

"We're responding to a current increase in green advertising claims," said FTC spokeswoman Jackie Dizdul. "We've been studying the marketplace, and a lot of companies are making green marketing claims. The last time our guidelines were updated was in 1998, and obviously a lot of things have changed since then."

An enormous variety of companies now make such claims. They include local utilities that charge premiums to subsidize wind power as well as car-rental companies and online marketers that sell certificates whose proceeds are said to pay for projects to reduce greenhouse gases. Other firms say they use premiums to plant trees, burn methane to convert it to less potent greenhouse gases, boost recycling or use so-called sustainable materials.

In a $55 million market that is largely unregulated, however, other companies have taken measures whose benefits are questionable.