Federal Trade Commission Chairman James C. Miller III said yesterday the agency could survive on a $50 million budget--$21 million less than a 1982 budget proposed earlier for the FTC--and admitted that as a result of cuts in this year's budget, morale at FTC is low.

The FTC has accepted a budget of $53 million for fiscal year 1984-- Just above the $51 million recommended by the administration-- and a budget of $58 million for 1983, although Miller refused to discuss those numbers since they remain a secret part of the budget negotiation process.

Speaking hypothetically, however, Miller said the agency could survive on $50 million, well below the $84 million recommended for 1984 by the Carter administration. Miller, who is beginning his third week at the agency, pledged the budget cuts and his efforts would result in a "leaner" FTC.

The commission has endorsed the 12 percent across-the-board cut recommended by the administration for fiscal year 1982, a figure that brings the agency's budget to $61 million.

"I'm convinced we'll be substantially more productive in the direction of doing things that are really in the public's interest," Miller said. "I do feel like, while there are probably minimum efficient sizes for agencies such as the FTC, we're not there yet.

"Contrary to what has been said by some, you will not come back a year from now and find that the agency is closed down," Miller said. "You will not find that the rate of output of cases has diminished substantially."

Nevertheless, he acknowledged "considerable anxiety about the budget" at the staff level. "There is anxiety about the new directions of the commission. I have tried to quell fears that the new team is going to pick out people and fire them on the spot.

"I have tried to persuade them that it's in their interests as employes to move in these new directions that the Congress has indicated . . . and the administration has indicated with its budget proposals and in nominating me to be chairman. Although it can't be done overnight, I think we will see a substantial improvement in morale over the coming months."

Miller, former architect of the administration's regulatory relief policy at the Office of Management and Budget, outlined his views about the agency during his first press conference yesterday. Miller said the agency under his leadership would:

Suspend temporarily its so-called line-of-business program, which requires companies to submit sales and profit data in major fields. "We need to take a breath to assess" the data since the program began three years ago, he said.

Emphasize horizontal price-fixing cases or potential antitrust violations among competitors. "We will go after those with considerable vigor," Miller said, noting the agency would "scrutinize very carefully horizontal mergers where it would result in significant aggregations of power."

Review its 11-year-old advertising substantiation program and ask the staff to determine how much the efforts add to product costs. The program requires advertisers to back up many of their claims. "Consumers are not as gullible as many people and many regulators tend to think they are," Miller said.

Miller said he did not expect the administration to address again the question of dual FTC-Department of Justice antitrust enforcement for the "next couple of years" or until the White House sees how the agency performs under his leadership. Earlier this year the White House proposed ending the FTC's antitrust mission by eliminating its Bureau of Competition, but congressional criticism forced the withdrawal of the proposal.

Miller said he would remain in contact with White House "friends and acquaintances" to "discuss policy matters from time." But Miller said that although the White House respects the FTC's independence, he thinks "there really are problems with the whole notion of independence," since such agencies are "not sufficiently responsive to Congress or to the executive branch."