Mr. Ensign denied any wrongdoing.

“Senator Ensign has stated clearly, he has not violated any law or Senate ethics rule,” said Rebecca Fisher, the senator’s spokeswoman. “If Doug Hampton violated federal law or rules, Senator Ensign did not advise him to do so, did not suggest that he do so, and did not cooperate with his doing so.”

Officials from the F.B.I. and the Senate ethics panel declined to comment.

P2SA, which has tried to turn Las Vegas into a national center for alternative energy, is co-owned by Greg J. Paulk, a contractor who has been a campaign donor to Mr. Ensign.

According to the e-mail messages, Mr. Ensign met with Mr. Paulk and Bob Andrews, then P2SA’s executive vice president, in May 2008 to discuss any help the senator might be able to provide on energy projects.

Image Douglas Hampton, once Mr. Ensign's administrative aide. Credit... Chris Schneider for The New York Times

At that time, Mr. Ensign was scrambling to find work for Mr. Hampton, his former top administrative aide. The senator had already helped find a position for Mr. Hampton at November Inc., a political consulting shop run by a former fund-raiser for the senator, and had spoken with donors at Allegiant Air and NV Energy about possible consulting work there.

At the meeting, Mr. Andrews said in an interview, he sought the senator’s support for a biodiesel facility the company was building in Las Vegas and a possible land swap in Sloan, Nev., with the federal Bureau of Land Management (referred to as BLM in e-mail exchanges) so the company could build a solar power plant.

Mr. Ensign brought up the idea of P2SA’s hiring Mr. Hampton, Mr. Andrews recalled.

The senator mentioned “that he might have somebody we should talk to who might be able to provide us with assistance in our biodiesel program,” Mr. Andrews said, adding: “I took this as a helpful hint.”