Mr. Visclosky, 59, was one of the lawmakers with the closest ties to PMA until its recent collapse. He relied heavily on the firm for campaign fund-raising, earmarked millions of dollars each year to its clients and maintained a close bond with a former aide who worked as a PMA lobbyist.  Mr. Visclosky is also a member of the Defense Committee’s appropriations subcommittee and an ally of Representative John P. Murtha, the Pennsylvania Democrat who is chairman of the panel and PMA’s best-known Congressional ally. Like other lawmakers linked to PMA by fund-raising and earmarks — most are Democrats — Mr. Murtha has said that he has no involvement in the inquiry and has not hired a lawyer.  Since the PMA investigation became public, Mr. Visclosky has fretted aloud that the inquiry may take a toll on his reputation for unblemished integrity in his home district in northwestern Indiana, a Democratic stronghold long notorious for political corruption scandals, Democratic House aides say.  Mr. Visclosky is the only lawmaker close to the PMA Group to endorse Republican calls for a House ethics committee investigation of its activities. He has promised to give away $18,000 in suspect campaign contributions linked to the firm, and he has also refiled his 2007 and 2008 campaign finance reports with numerous small corrections.  And in a recent meeting of the senior House appropriators about proposals to curb their traditional power to grant earmarks, individual members’ pet projects inserted into spending bills, Mr. Visclosky surprised his colleagues by voicing support for the idea, Democrats said. And he appears to have dropped all PMA clients from his list of earmark requests for the 2010 fiscal year, which had to be posted online this week.  But the two-way flow of money — campaign money from PMA to Mr. Visclosky, and earmarks from Mr. Visclosky to PMA clients — had been raising concern in both Washington and Indiana long before the investigation became public.  He has received more campaign contributions than any other lawmaker from PMA employees since 1989 — about $270,000, according to an analysis by the Center for Responsive Politics, which tracks campaign finances.  And in the last election, nearly 20 percent of the money he raised for his campaign and political action committee, $370,000, came from the PMA Group and its clients. More than two-thirds of that came during the two-month periods in 2007 and 2008 when Mr. Visclosky was completing his annual earmark requests.  Meanwhile, over the last two years, Mr. Visclosky personally directed more than $33 million in taxpayer money — nearly a quarter of the earmarked money he obtained — to clients of the lobbying firm, according to data compiled by Taxpayers for Common Sense, which tracks earmarks.  One Visclosky project has attracted special attention from critics as an example of the cozy ties among the lawmaker, the firm and its clients: the Purdue Technology Center of Northwest Indiana. Mr. Visclosky created the nonprofit center with more than $7 million in earmarks beginning in 2002, saying it would encourage entrepreneurship in his economically depressed district. But its federally subsidized facilities were quickly filled by branch offices of established government contractors who are clients of the PMA Group.  The Capitol Hill publication Roll Call reported two years ago that of the center’s seven charter tenants, five were PMA clients whose employees contribute heavily to Mr. Visclosky’s campaigns. Of the five, only NuVant Systems, a fuel cell company started by a chemistry professor, had its headquarters in Mr. Visclosky’s district. Two others — the Sierra Nevada Corporation, based in Nevada, and ProLogic, based in West Virginia — are each also reported to be embroiled in federal investigations involving their earmarks. (The center has now signed more than a dozen other non-PMA clients.)  The son of a former mayor of Gary, Ind., Mr. Visclosky was first elected to Congress in 1984. He has rarely faced serious opposition to his re-election. But he routinely raises big sums, like the more than $2 million his campaign and political action committee brought in last election.  He donates the vast majority of the money to other Democrats, an important source of political clout. Like other senior members of the Appropriations Committee, he is believed to aspire to its chairmanship, one of the most powerful positions on Capitol Hill.  Though his district has a history of political corruption, Mr. Visclosky has long held himself apart, even once sponsoring a good-government study to find ways to improve the efficiency of local government offices, a move that put him at odds with local Democrats angry at the interference with their turf.  But his efforts at reform have had blind spots: his good-government study, for example, was paid for by private companies in the steel and energy businesses who have interests before him in Congress.  The PMA raid and the spotlight it has put on Mr. Visclosky have so far caused few political ripples in northwest Indiana.  George Van Til, the Lake County surveyor and a Democrat, recounted Mr. Visclosky’s recent pledge to help solve a flood-control problem in a subdivision of Gary.  “People appreciate what he does here,” Mr. Van Til said. “I sat down with his staff two weeks ago, and when they walked away, I had a commitment for $1.2 million for flood relief.”  He added, “Unless someone tells me differently — that he’s doing something wrong — I think he’s doing something right.”  A version of this article appears in print on , on Page A11 of the New York edition with the headline: Indiana Lawmaker’s Name Is Said to Surface in Inquiry Into Lobbying Firm. 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Prosecutors’ interest in Peter J. Visclosky, a Democrat with big influence over federal spending, is the clearest sign yet that the investigation of the PMA Group may spread to Capitol Hill.