President Carter's public advocate appointers say they like their new jobs. They are plowing ahead with new plans, and progressive visions, despite bureaucratic restraints and outmoded civil service regulations, and they say the President welcomes their dissenting opinions.

But some of the veterans of previous administrations say that they've heard it all before, and that simply bringing a few people into the top echelons of government isn't likely by itself to make much difference in the ways things are run.

These were among the conclusions that emerged from a conference here yesterday by Ralph Nader's Public Citizens Forum to monitor the progress of former members of public advocacy groups now running or working in the agencies they used to criticize from outside.

The conference also witnessed a continuation of the split in consumer ranks between Nader and Joan Claybrook, his former close friend and ally, now administrator of the National Highway Traffic Safety Administration. In a blistering attack several weeks ago, Nader demanded her resignation for failing to live up to promise to reform the agency and for allowing the auto industry on "unheard-of" delay in phasing in safety features, such as airbags, until 1982.

He renewed his criticism in an interview yesterday, saying that Claybrook's acquiescence in that decision and others "crippled her ability to regulate the industry."

"People in government can't be treated differently because they were once in the consumer movement," Nader said. "Our job is to maintain an arm's length and make sure former colleagues earn respect for what they do in office, not what they did before they got there."

Claybrook, one of the panelists, replied indirectly: "If you take to battle too often or on issues you can't win, you dissipate your support, your staff's support and the ability to get continued support."

In an interview after the conference, she said Nader had scored some points, but hadn't gone about it in a very pleasant way:

"Ralph is good at raising a public fuss, and he did. He hit the high points and put the agency staff on notice that if they are lax they'll hear about it. I don't object to that . . . But no one likes to be the object of criticism, particularly criticism that you lack courage."

At the conference, most of the recent appointees stayed away from such issues as how to ease institutional restraints to increase performance, or how the job differed from their expectations. Most simply recited lists of recent initiatives or accomplishments and told of how much fun they were having, and some described the problems caused by an already entrenched bureaucracy.

The other panelists included Sam Brown, director of ACTION, the umbrella public service agency: Carol Tucker Foreman, an assistant secretary of agriculture and former head of the Consumers Federation of America; Michael Pertschuk, chairman of the Federal Trade Commission; Gus Speth, of the Council on Environmental Quality, and Harrison Wellford, executive associate director for reorganization of the Office of Management and Budget.

A subsequent panel of former high officials was somewhat skeptical of what the first panel had to say.

"The idea that you can bring a few people into the superstructure and make a difference is ridiculous," said Ramsey Clark, Attorney General under President Johnson. "Bureaucrats who have been there have seen 15 or 20 of you come and go. What you've got to do is motivate them, because those are the people who make a difference."

Morton Halperin, a senior staffer on President Nixon's National Security Council, said what he heard yesterday sounded like what he heard at the end of 1969, when national security adviser Henry Kissinger told his Harvard friends that everything would work out but that it was too soon to make any judgements. Halperin advised current bureaucrats to avoid being drowned in bureaucracy, not to be bound by limits of "supposed authority," and to work on one small project that could be accomplished and have an effect.