WASHINGTON — A decade-long boom for corporate lobbyists in Washington may be quieting down, just as tougher congressional rules for the multibillion-dollar industry take effect next year.

The new rules mandate more detailed disclosure of lobbying activities, industry oversight by the Justice Department and penalties of up to $200,000 for violations. They will force corporations and trade groups to provide more precise spending records and to take a harder look at who's lobbying for them.

Reports for spending in the second half of 2007 are due by Feb. 15. But under the new rules, which take effect Jan. 1, lobbyists and companies must now file quarterly reports.

The lobbying reforms come as corporate spending habits appear to be shifting. Since the late 1990s, expenditures grew by about 80 percent and, in some years, at an annual clip of 12 percent, according to the Center for Responsive Politics, a watchdog group.

K Street's river of cash hit record levels in 2006, as its two main tributaries, corporations and trade associations, helped bring the high-water mark to a record $2.63 billion in reported spending. Corporations and trade groups accounted for roughly 70 percent of that. Unions, professional associations and other organizations comprised the remaining 30 percent.

But in the first six months of 2007, spending — based on disclosure reports filed with Congress — reached $1.34 billion, only 2.3 percent higher than the same period last year.

A slower pace, but still an impressive amount of influence, coming in from myriad sources, to monitor. The new rules are meant to do just that.

"The increased precision in the reporting requirements may reduce the overall amount that is reported because currently people are over-reporting lobbying income and expenses," said attorney Craig Engle, a registered lobbyist with Arent Fox LLP.

He expects a smaller community of lobbyists with a slightly slower spending rate.

That prediction isn't shared across the industry. Several experts and lobbyists said that no one really knows what impact, if any, the rules will have on spending. Some experts said lobbyists might expand their repertoire to activities they aren't required to disclose, such as "grassroots" campaigns and advertising.

There are nearly 36,000 registered lobbyists, more than double the number in 2000, according to the Senate public records office's most recent estimate. Some experts say that number is inflated by duplications and outdated registrations.

The new lobbying rules — an outgrowth of corruption scandals involving lobbyist Jack Abramoff and several U.S. lawmakers — are designed to enhance transparency, not curb lobbying. They take effect Jan. 1.

James Thurber, an American University professor, calculated that about 84,000 people work in the business — including lobbyists, their staff, pollsters and others — which, he says, is the third-largest Washington industry behind government and tourism.

Thurber, who has testified before Congress for reforms, said there still isn't enough transparency.

Wielding influence through grassroots campaigns, coalitions, advertisements, conferences, surveys and papers, thousands are not counted as lobbyists. That's an oversight, Thurber said, that the new rules fail to address. Some might even finagle an invite from a lawmaker to a meeting to avoid having to register as a lobbyist, he said.

"They're going to be more and more creative about this," he said.

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