Corporations, unions and other interests spent a record $2.79 billion in 2007 on lobbying Washington officials, said a study from a watchdog group. The group, the Center for Responsive Politics, said spending in 2007 eclipsed the previous record in 2006 by $200 million, with health care interests, Wall Street, the real estate industry and insurers among the biggest spenders. Sharply higher spending was seen on other fronts, with the private equity firm Blackstone Group increasing its expenditures 477 percent to $5.4 million. The private equity industry halted an effort in Congress recently to raise taxes on the profits of its senior partners.