As lawmakers prepare to consider a $410 billion spending bill carrying pet projects for clients of a lobbying firm under FBI investigation, the House will vote as early as Tuesday on whether to start an ethics investigation into the relationship between earmarks and campaign contributions.

The vote could put majority Democrats and at least a few Republicans in an uncomfortable spot. They will have to choose between authorizing the House ethics committee to investigate the most delicate of political relationships or publicly voting against such a probe.

The action comes as House Democrats are trying to pass a massive fiscal 2009 omnibus spending bill (HR 1105) that carries thousands of earmarks, including several for clients of The PMA Group, a lobbying firm that is disbanding in the wake of an FBI raid of its offices and an investigation into whether it used straw donors to circumvent campaign finance laws.

The pitcher of this political curveball is Rep. Jeff Flake , who introduced a resolution late Monday that calls for an ethics investigation into “the relationship between earmark requests already made by members and the source and timing of past campaign contributions.” Flake’s resolution qualifies as “privileged,” meaning it has priority status for floor consideration.

Flake, an Arizona Republican who has become the scourge of congressional earmarkers, cited numerous recent news stories about PMA’s campaign contributions, its ability to secure earmarks for clients and the FBI probe into whether it complied with the law in making donations.

The resolution, which the House must dispose of by Wednesday, would instruct the Committee on Standards of Official Conduct, as the ethics panel is known, to report its findings within two months.

Often when a privileged resolution involves a politically thorny issue, the majority party will move to table — or kill — the measure. The roll call vote probably will be on the motion to table Flake’s resolution rather than the measure itself.

The timing of Flake’s call for a vote could hardly be less auspicious for Democrats. A list of Democratic-sponsored earmarks in the omnibus that are targeted to clients of PMA was circulating Monday night on Capitol Hill.

Flake’s office released a compilation of eight earmarks worth $7.7 million in the bill. Taxpayers for Common Sense, a watchdog group, sent out the same list and identified the individual sponsors of the earmarks as Reps. Peter J. Visclosky of Indiana, Tim Ryan of Ohio, John B. Larson of Connecticut, Brad Sherman and Jane Harman of California, Stephen F. Lynch of Massachusetts and Emanuel Cleaver of Missouri. Reps. Mike Doyle and Jason Altmire , both of Pennsylvania, were identified as cosponsors of one earmark.

All but one of those earmarks is in the section of the bill written by the Energy and Water Appropriations Subcommittee, which is headed by Visclosky.

With $219,000 in checks to his political committees since 2001, Visclosky is the leading recipient of campaign contributions from PMA’s political action committee and its employees, according to a review by CQ MoneyLine.

Doyle and Ryan ranked among the top 10 House members in PMA contributions.

Larson, Altmire and Sherman were in the top 40, receiving between $15,500 in Sherman’s case and $37,850 in Larson’s case. Harman and Lynch have each received more than $10,000 in PMA contributions over the years.