Lobbying activity plunged in 2011 for the first time in a decade, most likely driven lower by the struggling economy and legislative gridlock on Capitol Hill, according to new estimates released Thursday.

The Center for Responsive Politics, which tracks money in politics, found that trade associations, multinational corporations and other interest groups spent about $3.27 billion on lobbying last year, down from $3.51 billion in 2010.

The number of registered lobbyists also dipped to 12,600, well off its peak of nearly 15,000 in 2007, the center reported.

The decline in official lobbying comes at a time when the profession is coming under fresh scrutiny in the presidential race, as GOP candidate Mitt Romney accuses his chief rival, Newt Gingrich, of making millions from “influence peddling” while claiming he wasn’t a lobbyist.

President Obama also revived his critique of the “corrosive influence of money in politics” during Tuesday’s State of the Union address, proposing a ban on lobbyists raising money for candidates.

After explosive growth beginning in the late 1990s, the official business of lobbying had been leveling off for several years, in part because of the economic downturn in 2008 and limits on lobbying enacted by the Obama administration, experts say. But 2011 marks the first year that the industry has retrenched, dropping about 7 percent in total dollars spent.

“The political gridlock in the 112th Congress has slowed the flow of money to K Street’s hired guns,” said Sheila Krumholz, CRP’s executive director.

The data in many ways reflect the ebb and flow of legislative priorities: The pharmaceutical and oil and gas industries, for example, spent significantly less last year than they had in 2009, when health-care reform and cap-and-trade proposals were front and center in Congress.

The television, music and movie industries, by contrast, posted record lobbying expenditures in 2011 amid roiling debates over piracy bills and other legislation. Internet giant Google, a relative newcomer to the Washington influence game, reported spending a record $11.4 million, much of which came during the final quarter of the year.

The National Association of Realtors also had a banner year, and the U.S. Chamber of Commerce remained the single largest lobbying entity in Washington — spending $66 million, an amount that includes the group’s local and state activities.

The center’s data are based on an analysis of lobbying reports filed with Congress last week; the numbers could change slightly as late-arriving reports are tallied, the center said.