WASHINGTON -- As in other states where hundreds of special interests vie for the attention of lawmakers and members of the executive branch, lobbying is big business in Ohio.

You just can't tell how big.

That's one of the conclusions drawn from a study released yesterday by a watchdog group that found special interests in Ohio and 33 other states spent at least $570 million in 2000 trying to influence legislation and affect agency rule-making.

Disparate and often lax reporting requirements make it impossible to track the full amount spent on lobbying at state capitols around the country, according to the Center for Public Integrity in Washington.

And in part-time legislatures where lawmakers have day jobs and sparse professional staff, the thousands of lobbyists and special-interest groups wield perhaps even more influence than their counterparts in Washington, the center has concluded from its study, "The Fourth Branch.''

"Disclosure laws are abysmal,'' said Diane Renzulli, co-author of Capitol Offenders, a book the center released in connection with the study.

"Until there's more sunshine in state legislatures, we'll never be able to paint a complete picture of the breadth and depth of conflicts of interest and influence in America's state capitols.''

The study compiled its figures from the 34 states that require the disclosure of lobby expenditures, including Ohio. Tennessee does not require lobbyists to report expenditures, while 15 states do require such reporting but do not compile overall lobby spending.

In 22 states, such as California, New York and Pennsylvania, comprehensive lobby-disclosure laws require reporting both lobbyists' spending and the salaries they are paid. In those states, the public can see how special-interest groups spend tens of millions of dollars annually to influence politicians.

Ohio, like other large states, has hundreds of special interests that employ lobbyists. But Ohio only requires the lobbyists to disclose their own expenditures -- so only the $390,000 spent in 2000 on such things as buying lawmakers meals or giving them gifts is accounted for in the state's total. Their salaries are not reported.

State Sen. Jeff Jacobson, R-Vandalia, proposed legislation in 1999 requiring more comprehensive disclosure of how much money special interests pour into lobbying in Ohio, but that bill was killed by legislative leaders and nothing similar has been introduced since.

Secretary of State J. Kenneth Blackwell was perhaps the most visible advocate of fuller disclosure, but he hasn't gotten far in effecting change.

The lack of comprehensive disclosure left Ohio ranked 30th in the amount spent by the lobbying industry among the 34 states that track overall spending -- even though the state ranked seventh in the number of special interests registered to employ lobbyists in 2000.

The past president of the Ohio Lobbying Association said there's no reason to mandate that lobbyists disclose their fees.

"There's no connection between what we are paid and whether that influences legislation,'' said Tom Green, president of Thomas Green and Associates. "The fact that one lobbyist might be paid twice as much as another is not a factor.''

Green advocates the elimination of limits -- effectively $50 per year on meals and $25 annually on gifts -- on what lobbyists can give to lawmakers as long as the amounts are fully disclosed. Taking a busy lawmaker to lunch or dinner is sometimes the only way to get the time to impart a position, he said.

"I don't know any legislators who sold their votes for the cost of dinner,'' Green said.

Nearly 37,000 special interests are registered to hire lobbyists in state capitols nationwide -- about five interest groups per state legislator.

The sheer numbers can overwhelm elected state officials, "80 percent of whom are part-time with little or no professional staff,'' said Charles Lewis, the center's director.

The center also asserts a potential danger of part-time "citizen legislators'' possessing built-in conflicts of interest when they consider legislation affecting their own profession -- unlike members of Congress, whose offices are their full- time jobs.

While the answer might not be to switch to full-time legislators paid higher salaries, the situation requires more disclosure by legislators about potential conflicts, Lewis said.

"If you are going to have citizen- legislators they have an added burden to maintain the public trust.''