A joint study by two political watchdog groups has found that Sen. Max Baucus -- the Montana Democrat who authored the principal health care reform bill being debated in the Senate -- was a major recipient of "contribution clusters" from lobbyists linked to health care groups.

The study, from the Center for Responsive Politics and the Sunlight Foundation, says members of Congress working on health care reform are receiving more money from the health industry than people realize.

This is because private lobbyists are donating to politicians who have already received donations from the groups those lobbyists represent, a practice the watchdogs describe as "contribution clusters."

The "never-before-seen" numbers, as the Sunlight Foundation describes them, show that Baucus collected contributions from 37 outside lobbyists representing PhRMA, the pharmaceutical industry’s chief trade association, and 36 lobbyists who listed biotech firm Amgen as their client.

In all, 11 major health and insurance firms had their contributions to Baucus boosted through extra donations from 10 or more of their outside lobbyists.

On Tuesday night, the Senate Finance Committee, which Baucus heads, voted down two proposals for a government-run public option for health care.

Baucus is third on the list for "contribution clusters" from the health industry, behind Senate Minority Leader Mitch McConnell (R-KY), in second place, and Arizona Sen. John McCain, who came in first -- though, as the study noted, McCain's donations were likely inflated by his presidential campaign last year.

View the full donations list here.

The watchdog groups have created a graphic called "Max Baucus' Wheel of Health Care Contributions," which shows the senator's largest health care donor is California-based biotech firm Amgen. That company gave Baucus $111,000 in the two-and-a-half-year period, by way of direct donations and no less than 36 other lobbyists.

In second place is PhRMA, the Pharmaceutical Research and Manufacturers of America, an industry group that represents drug makers. They gave Baucus nearly $89,000 by way of 37 lobbyists. Among PhRMA's members are pharma giants AstraZeneca, Merck and Pfizer, all of whom also donated directly and by way of "contribution clusters" to Baucus.

"There is no indication that the extra giving by lobbyists was part of a planned effort by the health care firms to solidify their support among key members of Congress," the Sunlight Foundation notes in an article published Thursday. "But whether coordinated or not, the newly-found clusters of lobbyist giving clearly illustrate the intensity of the full-court press that the industry is currently waging on Capitol Hill."

-- Diane Sweet contributed to this report