Robert J. Keeshan, a.k.a. Captain Kangaroo, made one of his rare postdawn appearances in Washington the other day when he went to Capitol Hill to talk about the sad state of television programming for children. He found Rep. Albert Gore Jr., a father of four young children, waiting for him.

Keeshan told him that "Captain Kangaroo," which helped raise several generations of children across the breakfast table every morning, is now being broadcast only at 6 or 7 a.m. on Saturdays and Sundays by CBS. "Gee, that's a really impressive commitment on the part of the network," said the Tennessee Democrat, who had only moments before labeled the state of television for children a tragedy. "Why have they done this to you, Captain Kangaroo?"

"The marketplace has come into play," answered Keeshan, who carefully explained that CBS lost millions over the years by airing a show for children, while the other two networks put on hugely profitable shows for adults. But in the end, he said, the economic pressures from the news departments and the affiliates proved too much.

"There has to be more than an economic reason for doing children's programming," Keeshan said. He agreed with Federal Communications Commissioner Henry M. Rivera that the number of shows for children has decreased in the past couple of years as a direct result of the Reagan administration's emphasis on deregulation by government. Rivera said the climate of deregulation has left networks with the perception that the FCC is not going to make a reasonable amount of children's programming a condition of licensing.

"One by one," said Rivera, "we have watched the best and the brightest programs disappear--'Captain Kangaroo'; 'Animals, Animals, Animals'; '30 minutes,'even the long-popular 'Wonderful World of Disney.' " He said he was "disheartened by the inaction" of the FCC and noted that FCC chairman Mark Fowler had recently suggested that the Public Broadcasting Corp. become the vehicle for providing children's programming while the administration proposes to slash PBC's federal funding.

Rivera suggested that Congress form a temporary commission of industry, government and the public to figure out how to resolve the conflict between the economics of the industry and its responsibility to the public. At the same time, he delivered to the subcomittee on telecommunications, consumer protection and finance, which was holding the oversight hearings, a letter from Fowler indicating that the FCC is going to reopen hearings into children's television.

An FCC task force concluded in 1979 that the industry was not "living up to its responsibilities," as Rivera put it, and while it held hearings into the issue in 1980, the FCC took no further action.

The agency's new interest comes shorly after Action for Children's Television filed a suit in the U.S. Court of appeals claiming that the FCC's failure to act on rulemaking in children's television was illegal. "I feel we managed to turn them around," said Peggy Charren, A.C.T. president, during a recess in Wednesday's hearing. Representatives of the networks brought film clips and anecdotal examples of the kinds of programming they were providing, but it was clear that cable firms such as Warner-Amex, which is offering Nickelodeon, a 13-hour-a-day channel for young people, are going after the market that commercial television doesn't particularly want. Warner-Amex president John A. Schneider said cable is currently offering 158 hours a week of children's programming, 91 of which are on Nickelodeon. He also said cable will be in about half the 83 million to 84 million television homes in America by 1985.

It has been 13 years since the FCC and the networks were first pushed to improve the product the commercial stations were offering children. And while the hearings were held in conjunction with national children's television week, only the network representatives seemed to think there was much to celebrate.

But self-regulation and programming by economic pressures alone may prove costly for the networks in the long run. Cable is doing what people such as Peggy Charren hoped for, namely providing viewers with diversified programming for children, something neither Congress, nor the FCC, nor the government, nor public pressure has been able to do. And while the FCC is getting back in the game, cable, at the rate it is going, may have left the marketplace that had no room for "Captain Kangaroo" far, far behind.