former commissioner Michael Pertschuk prominent among them -- who would argue that the Federal Trade Commission has been a much different place under the Reagan administration than it was under previous administrations.

Pertschuk and other critics argue that President Reagan's appointees to the FTC, including Chairman James C. Miller III, have effectively de-clawed the commission, eliminating many of the do-good functions that had made it, in their eyes, a strong champion and protector of consumer rights.

Miller and his peers, of course, would argue differently. The commission staff has prepared a digest of the achievements of the commission's new age, entitled "A Progress Report on the First Three Years of Reagan Administration Leadership: October 1981 to October 1984."

The slim, orange volume, published internally, is a largely laudatory look at the FTC's actions over the past three years. From the opening paragraph it sets out the fundamental differences between this commission and the ones that preceded it.

"The cornerstone" of this commission's philosophy, the report says, "has been the recognition that a well-functioning marketplace provides the most effective protection for consumers. Government regulation is simply no substitute for a competitive marketplace . . . . "

As examples of how the FTC has changed its ways, the report cites the agency's new emphasis on informing both businesses and consumers about the law, more carefully targeted enforcement programs, and efforts to avoid litigation by settling complaints or using other means to resolve disputes. The report insists the commission is as strong a protector of consumer rights as ever, if not stronger.

But most of the achievements that the report lists are also cited by commission critics as examples of ways in which the FTC has turned away from its old, consumer-oriented approach. So great are the philosophical differences between the followers of Pertschuk and Miller that what one side sees as progress, the other necessarily will view as quite the opposite. POLICY ON ANTITRUST. . .

The report devotes a great deal of space to the commission's work in antitrust cases, reaching the conclusion that "the commission's antitrust program is grounded on basic law-enforcement principles, such as a systematic attack on horizontal restraints and a consistently applied merger policy that emphasizes lower prices for consumers. This effort promises continued large payoffs in the future."

Last week Miller elaborated further on the notion of using antitrust enforcement to hold prices down in a speech before the Society of Independent Gasoline Marketers of America in New Orleans. Shedding some light on the FTC's controversial decisions earlier this year to approve the oil-industry takeovers of Getty by Texaco and Gulf by Chevron, Miller said the FTC is following an evolutionary path of antitrust law that began in the mid-1970s.

"At one time, antitrust enforcement officials as well as the courts seemed to view market concentration as the beginning and end of merger analysis," he told the oilmen. "Little attention was given as to just how the merged firm would affect the industry's ability to raise or lower prices and restrict or enhance output. You know better than I that competition is a lot more complicated than the number of gas stations in a given neighborhood."

In the case of Chevron-Gulf, he said, the commission particularly focused on overlapping operations of the two companies in the southeastern United States. The commission found, he said, that the plethora of Chevron and Gulf gasoline stations in the region did not matter much, because an attempt to use the large number of stations to organize a price increase would only bring new station operators into the market to cash in on the higher prices, thus pulling the prices down.

The greater problem, he said, lay in a potential lack of competition at the wholesale level and the far-flung nature of the gasoline business in the region. That would allow wholesalers to raise prices in a locality that could not, for logistical reasons, buy cheaper gas from a supplier in another area, he said.

Those were among the grounds, he said, on which the FTC forced Chevron to sell Gulf's southeastern marketing operations, while allowing the rest of the $13.3 billion merger -- the biggest in history -- to go through. To Miller, and to the Justice Department's antitrust chief, J. Paul McGrath, bigness alone apparently does not necessarily equal badness.

"I have noted a definite trend concerning oil mergers," Miller said. "It is not toward substantially higher concentration of control of our crude oil reserves or any accretion of market power. Instead, it is a trend toward higher levels of uncertainty about the industry's future, and confusion about the role of antitrust agencies in making sure the industry remains competitive."