"In fact, the scale of our combined company will help us to innovate even faster and accelerate the deployment of services such as increased broadband speeds and expanded TV options," Time Warner Cable said in a statement to Reuters.
Comcast spokeswoman Sena Fitzmaurice said in a separate statement that the transaction would bring consumers benefits such as faster Internet speeds, better programming choices and lower costs, "all things that we think consumers will like."
The U.S. Senate Judiciary Committee has scheduled a hearing on the cable merger for April 9.
American Airlines said in a statement: "We are taking the best of both US Airways and American Airlines to create a formidable competitor with an expanded network that provides a real choice for global and domestic travel."
(Read more: Comcast CEO: TimeWarner Cable deal 'pro-competitive')
Many with no opinion
The poll found a significant share of people who did not state a strong opinion about the mergers. For the cable deal, 26 percent said they did not know how they felt, while for the airline deal, 28 percent said they did not know.
Clark said those numbers were above average for a poll about public affairs.
"People are acknowledging that this isn't something that they have enough knowledge about to have a strong opinion," she said.
Although mergers receive significant media attention, antitrust enforcement has not regularly been in the U.S. headlines since a long-running government battle with Microsoft beginning in the 1990s.
U.S. mergers and acquisitions above a certain size must be submitted for review to antitrust enforcers, who may seek to block a deal if they believe it would be anticompetitive.
The enforcers at the U.S. Justice Department and the Federal Trade Commission (FTC) try to promote competition in other ways, including criminal investigations into cartel price-fixing or civil inquiries into alleged collusion.
(Read more: Biggest losers in the Comcast-Time Warner Cable deal)
Asked in the poll to evaluate how the federal government was doing preventing monopolies and ensuring competition, 30 percent said they approved and 42 percent said they disapproved. Twenty-eight percent said they did not know.
The answers revealed a significant partisan split, as Democrats approved of the government's job by a 45-33 margin and Republicans disapproved by a 56-23 margin. Enforcement policy has been under the control of Democratic appointees of President Barack Obama since 2009.
An FTC spokesman and a Justice Department spokeswoman declined to comment.
Despite the dissatisfaction, the poll found no consensus about companies that ought to be broken up.
Asked to name a company or industry in the United States where there was an illegal monopoly, common answers included none, government, cable, oil, Microsoft and banking.
Thousands of lawyers, economists and other antitrust experts are converging in Washington, D.C., this week for what is billed as the largest conference on competition law in the world. The meeting of the American Bar Association's antitrust section runs through Friday at a hotel two blocks from the White House.