Some corporate lobbyists, speaking anonymously for fear of irking the White House, said they were revising job descriptions in light of the administration’s decision to bar registered lobbyists from sitting on industry advisory panels. “Wait a minute, who is going to be on this board?” a lobbyist for a major aviation company recalled thinking. “Are we going to actively manage people to not be lobbyists?”

The pattern has set off a debate on K Street and Capitol Hill. Many lobbyists argue that the decline in registration demonstrates the unfairness of cracking down on their trade while ignoring the campaign contributors, corporate executives, union chiefs and others who seek the ears of public officials. Advocates for the rules, on the other hand, argue that they should be tighter still, with tougher enforcement.

“In a world of two and a half years ago,” said Thomas M. Susman, director of government affairs for the American Bar Association, “people in Washington would have said: ‘If in doubt, register. I like the publicity. I like to be in periodicals that list lobbyists. I want to be able to tell potential clients how many I am already registered for.’ Those are people who I believe have reconsidered.”

“To the extent that people now say the Obama restrictions and prohibitions are driving lobbyists underground and having a perverse effect, in a sense that is right,” Mr. Susman said. “But if you want more people to be disclosed as lobbyists, well, change the law and require them to disclose.”

Of course, even before the new rules, there were some public policy advisers who avoided registration while nonetheless profiting handsomely by helping private clients influence Congress and the White House. Under the Obama administration, the most conspicuous example is Tom Daschle, the former Democratic Senate leader. He advises colleagues and private clients on health care policy as a member of the lobbying firm DLA Piper. And he also informally consults on health care policy with Mr. Obama, senior White House officials and former Senate colleagues. But he is not registered as a lobbyist. (Mr. Daschle has said he complies with all the rules.)

Advocates of stricter disclosure requirements say they want the rules extended to cover policy advisers like him. Ms. Miller, of the Sunlight Foundation, said her organization was working to lower the registration requirements to cover anyone spending even a “de minimus” amount of time on lobbying.

“There are influence peddlers who have gotten away with not disclosing because they are under the 20 percent rule,” she said, “and we want to shut down that loophole.”