When Jim McCrery, a former Louisiana congressman, urged lawmakers last month to pursue entitlement cuts and tax reform, he was introduced on television as a leader of Fix the Debt, a group of business executives and onetime legislators who have become Washington’s most visible and best-financed advocates for reining in the federal deficit.

Mr. McCrery did not mention his day job: a lobbyist with Capitol Counsel L.L.C. His clients have included the Alliance for Savings and Investment, a group of large companies pushing to maintain low tax rates on dividend income, and the Win America Campaign, a coalition of multinational corporations that lobbied for a one-time “repatriation holiday” allowing them to move offshore profits back home without paying taxes.

In Washington’s running battles over taxes and spending, Mr. McCrery and his colleagues at Fix the Debt have lent a public-spirited, elder-statesman sheen to the cause of deficit reduction. Leading up to the fiscal negotiations, they set up grass-roots chapters around the country, met with President Obama and his aides, and hosted private breakfasts for lawmakers on Capitol Hill. In recent days, Fix the Debt has redoubled its efforts, starting a new national advertising campaign and calling on Mr. Obama and Congress to revise the tax code and reduce long-term spending on entitlement programs.

But in the weeks ahead, many of the campaign’s members will be juggling their private interests with their public goals: they are also lobbyists, board members or executives for corporations that have worked aggressively to shape the contours of federal spending and taxes, including many of the tax breaks that would be at the heart of any broad overhaul. While Fix the Debt criticized the recent fiscal deal between Mr. Obama and lawmakers, saying it did not do enough to cut spending or close tax loopholes, companies and industries linked to the organization emerged with significant victories on taxes and other policies.