Lobbying experts also say there are other gaps in the campaign’s lobbying guidelines. Lobbyists can try to influence lawmakers on behalf of corporate and other clients without registering, as long as the time they spend doing so does not exceed a specified threshold. They are also often not required to register if lobbying overseas on behalf of foreign politicians or companies.

“Influential people with fat Rolodexes can in effect lobby without having to register,” said Sheila Krumholz, the executive director of the Center for Responsive Politics, a nonpartisan center that studies money in politics.

In recent years, for instance, Mr. Davis’s business partner, Paul J. Manafort, has met with the United States ambassador in Ukraine, a time when he was advising Viktor Yanukovich, that country’s onetime prime minister, a State Department official said. Mr. Yanukovich’s party was opposed by both the Bush administration and Mr. McCain because it was closely tied to Vladimir Putin.

If Mr. Manafort had met with United States officials in this country on behalf of the Ukrainian politician, he would have had to register. But some meetings abroad are not covered, several legal experts said.

Mr. Davis, who worked as deputy campaign manager in Bob Dole’s 1996 presidential campaign, has been a registered lobbyist for telecommunications companies like SBC Communications, Comsat and Verizon. Some of his other registered clients have included Deutsche Post World Net USA, the giant cargo concern, and GTech, a worldwide lottery firm.

Mr. McCain’s campaign said Mr. Davis still retains a stake in his lobbying firm, Davis Manafort, but is not receiving profits from it.

But a look at Mr. Davis’s activities surrounding Imagesat shows how the business ties and financial interests of lobbyists can be complex.

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Back in early 2004, Mr. Davis and Mr. Manafort started discussing becoming consultants with Pegasus Capital, based in Cos Cob, Conn. Not long afterward, the two men were providing advice to Pegasus about governmental matters that might affect companies in which the firm had invested and also suggested investment targets. The firm has never retained Davis Manafort as a lobbyist.

In late 2004, however, Mr. Davis became a registered lobbyist for Imagesat. He gained the account through a recommendation from Pegasus, which holds a stake in the company, said a person knowledgeable about the investment firm who spoke on the condition of anonymity. Mr. Davis said he found the firm without Pegasus’s help.

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Davis Manafort received $120,000 from late 2004 to mid-2005 to lobby for Imagesat on both defense and domestic security issues. Mr. Davis and Christian Ferry, now Mr. McCain’s deputy campaign manager, were the two lobbyists on the project, the records show.

Early in 2005, Mr. Davis tried to develop another relationship with Pegasus when he and two other men suggested that it help bankroll a proposed new private equity firm. That firm was to focus on investments in domestic security companies, including those that vied for federal contracts, the person knowledgeable about Pegasus said.

A draft proposal for the new firm described Mr. Davis as a power player among Washington influence brokers.

“For the last three decades in the White House, Congress, federal agencies and politics both here and abroad Rick has operated at the highest level of decision and deal making,” according to a copy of that proposal reviewed by The New York Times.

Along with his work as a lobbyist, Mr. Davis at the time was also drawing a salary as the part-time president of the Reform Institute, a Washington group that Mr. McCain helped found to reduce “the influence of special interests” in politics and government.

The proposed firm never took off. But Pegasus also offered another opportunity to advisers, like Mr. Davis and Mr. Manafort, who worked with it — the chance to get in on some of its investments. In November 2005, Pegasus bought a stake in a company called Traxys, which trades in industrial metals.

In January 2006, just two months later, the subject of metals trading came up in association with a social meeting Mr. Davis helped arrange near Davos, Switzerland. At that meeting, first reported by The Washington Post, Mr. McCain met the Russian aluminum magnate, Oleg Deripaska, who has been barred from entering the United States apparently because of alleged criminal ties.

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After the event, Mr. Deripaska sent a brief thank-you note to Mr. Davis and Mr. Manafort. In it, he said, “Please will you send me the information on the metals trading company we discussed and would be happy to see if I can do anything to help.”

In written responses to questions, Tucker Bounds, a spokesman for the McCain campaign, said that “Mr. Davis did not approach Mr. Deripaska” about any metals trading company. Mr. Bounds said Mr. Davis retained investments he made during the time he advised Pegasus, a relationship that ended in 2006. He said Mr. Davis declined to disclose whether Traxys was one of them because he considered the investments a private matter.

A spokesman for Pegasus said it was unaware of the letter from Mr. Deripaska and had had no business dealings with him. A spokesman for Mr. Deripaska said he had never hired Davis Manafort. Mr. Manafort did not return phone calls.

Davis Manafort has worked for other overseas clients for whom it did not have to register, including the richest man in Ukraine, Rinat Akhmetov. One Mr. Akhmetov’s companies, SCM Holdings, hired the firm to help it develop a corporate communication strategy, a spokesman for Mr. Akhmetov said. That relationship lasted until September 2005.

Mr. Akhmetov was the principal financial backer of Mr. Yanukovich, the Ukranian politician for whom Davis Manafort has also worked.