But nowhere in these statements does Mr. Manne directly disclose that Comcast is among a small group of donors that finances his nonprofit group, a fact that Mr. Manne confirmed in response to a question late last week.

“We are no value to our donors or ourselves unless we maintain our independence and academic rigor,” he said, before adding that “maybe there is some subconscious thing there.”

Mr. Manne’s group is hardly alone.

Letters detailing the benefits of the Comcast deal were submitted to the Federal Communications Commission by staff members from Americans for Tax Reform, the American Enterprise Institute, the Institute for Policy Innovation, Competitive Enterprise Institute, the Free State Foundation and the Center for Individual Freedom, as well as by a professor at a technology program at the University of Pennsylvania, all of which received support from Comcast or its trade association, tax documents and other disclosures reviewed by The New York Times show.

A similar pattern is evident with charities like the Urban League and more than 80 other community groups that supported the media company and that also accepted collectively millions of dollars in donations from the Comcast Foundation over the last five years, documents reviewed by The Times show. The Greater Philadelphia Hispanic Chamber of Commerce, for instance, received $95,000 from Comcast over the last three years.

What is clear is that Comcast has tried to make the most of these endorsements. Varsovia Fernandez, the president and chief executive of the Hispanic Chamber of Commerce, wrote a letter to the Federal Communications Commission, as well as a commentary piece in The Philadelphia Daily News, titled, “Comcast Deserves a Fair Shake.”

The company maintains a list on its website of organizations that have sent in endorsements, and at times issues news releases and sends Twitter messages to make sure they are noticed. The list includes dozens of state and local officials, many of whom have received financial support from Comcast. The company has contributed millions to candidates in state elections in the last four years, including $15,000 to Governor Bryant of Mississippi, whose spokeswoman said his positive words about the company had nothing to do with the donations.

Representative Tony Cárdenas, a California Democrat who is one of the few lawmakers in Washington to take a definitive stand on the deal — he opposes it — said that the relative silence from members of Congress did not surprise him. He said the deal was bad for the country and would result in a single company with too much control over cable television and the Internet.