Comcast’s Brian Roberts and NBC Universal’s Jeff Zucker faced withering criticism Thursday that combining the two media titans would stifle independent production and do little to foster diversity on the air.

Comments came during a House Judiciary Committee hearing on the proposed Comcast-NBC U merger.

As at two previous hearings earlier this month, lawmakers took the opportunity to raise an array of concerns about Comcast’s acquisition of a 51% stake in NBC Universal, even veering into the content of NBC’s programming. Rep. Maxine Waters (D-Calif.) specifically chided Zucker on why there were not more African-American shows and characters on the Peacock.

Although some committee members gave indications of support for the deal to Roberts, chairman and CEO of Comcast, and Zucker, prexy and CEO of NBC U, several vocal critics also were at the hearing, including Jean Prewitt, head of the Independent Film & Television Alliance, and Larry Cohen, prexy of the Communication Workers of America. At the urging of Rep. Sheila Jackson Lee (D-Texas), Roberts and Zucker agreed to meet with Prewitt and Cohen.

Prewitt argued that Comcast’s commitment to increase the number of independently owned channels on its cable systems hardly means it will boost the health of independent producers. Moreover, she expressed skepticism that Comcast’s Fancast Xfinity service, a broadband platform for Web streaming of cable programming, would be open to a substantial amount of independent content.

“Our experience in general is that the broadcast networks are now wholly unavailable to truly independent programming, unless they are producing reality series,” Prewitt said.

Roberts told the panel that the company is committed to adding at least two new independently owned channels to its cable systems beginning in 2011, and noted that on-demand viewing platforms offer new opportunities for independent projects. Zucker noted the benefits of the merger will come with Comcast’s overall commitment to invest in programming, a move he said will strengthen the broadcast business.

Rep. Howard Berman (D-Calif.), whose district includes Universal Studios, also expressed concerns over access to distribution for independent producers. But he said that one of the “appeals” of the combo was the expectation of few layoffs. “This is a jobs issue for me, in a very real sense,” he said.

Cohen had predicted that a loss of jobs would follow the merger, citing what he claimed was an antilabor stance following Comcast’s acquisition of AT&T Broadband in 2002. He lamented that CWA has not been granted a meeting with Comcast since that deal to discuss its concerns. Roberts, who vigorously denied taking any such position, said, “We don’t believe there is any commitment that we made that was not kept at the time of that merger.” Roberts said he looks forward to a positive relationship and “a new beginning” with labor.

Zucker even alluded to the planned cuts of at least 300 staffers at ABC News as a sign of the woes of the broadcast business. Zucker and Roberts reiterated that the merger will bolster the Peacock’s broadcast network because it will have a deep-pocketed owner with roots in the TV biz. And because there is so little overlap in the operations of the cable giant and the Peacock, there will not be large-scale layoffs after the merger is completed.

“I am gratified by the fact that this is not about synergies or anything of that sort,” Zucker said.

In response to Waters, Zucker offered assurances that diversity is one of his top priorities. But Waters said that she was troubled by what she characterized as the state of NBC U programming.

“Let me say that it is very difficult to accept that you cannot find the kind of program I’m talking about (on your schedule),” she said. “It is unacceptable to say you don’t know when it will happen. I don’t think black viewers would like to hear that kind of answer.”

Another witness, Mark Morial, prez of the National Urban League, said the league has not taken a formal position but does worry about diversity issues.

Zucker was also asked his reaction to FCC chairman Julius Genachowski’s announcement that the FCC would recommend that 500 megahertz of spectrum be made available for mobile broadband. Much of that would come from the broadcast spectrum. Zucker said that while he supports the FCC’s goals, he questioned the wisdom of targeting broadcasting’s spectrum allotments.

Other witnesses at the hearing included activists Andrew Jay Schwartzman, prez of Media Access Project, and Mark Cooper from the Consumer Federation of America. The two resumed their respective assaults against the merger on competitive grounds, especially the impact of program bundling by the cable giant.