Few issues before the Federal Trade Commission have stirred as much public comment lately as the commission's proposal to let supermarkets advertise items they don't have in stock. And most of the comments have been negative.

By the end of the official comment period last week, the commission had received more than 2,400 letters on the issue, most of them opposed to the proposed rule change, according to a woman speaking for the FTC. But she said that many of the writers were misinformed about what the commission is proposing -- a criticism that commission officials have leveled also at press reports on the subject. She said many of the letters say the FTC is about to condone "bait and switch" tactics, which she said is not so.

Many of the letters mention a widely circulated Miami Herald editorial that commission officials say was wrong about the gist of the proposal. Commission staffers insist that all they want is to reduce the amount of inventory that stores are required to carry and to eliminate a requirement that supermarkets document their stocks of sale items. Other laws still on the books, they say, will prevent the markets from abusing customer faith in advertisements. (The rules that would be changed do not apply to other types of stores.)

Consumers aren't the only ones who are concerned about the proposal. A group of 35 state attorneys general has expressed its opposition. "There can be no substitute for truthfulness in advertising," Iowa Attorney General Thomas J. Miller wrote in a letter signed by the rest of the group. "If the commission embarks on a course to rescind the rule, it will send a clear message to business that the commission attaches no value to truthfulness in commercial relations. This is the message that is both offensive and frightening for it perverts the commission's legitimate objectives and invites the victimization of the public that this commission is supposed to protect . . . .

"The rule under consideration has served the public effectively and should not be altered," Miller added. "If anything, the commission should consider expanding the rule to include other retail businesses and thereby further protect consumers from false and deceptive advertising."

The commission staff is to analyze the pile of comments and make a recommendation to the commission in about a month. STALEMATE. . .

The FTC's prolonged lack of a formal reauthorization by Congress has become a real thorn in the side of Chairman James C. Miller III. The commission "has lived by a series of continuing resolutions and appropriations" for the past two years, Miller complained in a speech this week. "There is no reasonable basis for delaying action on the FTC's authorization any longer."

Miller may not have to wait much longer. Congressional sources say that the agency's reauthorization may pass this session -- but House Democrats may use it as a vehicle to try to change the agency's course a bit.

Critics complain that, under Miller, the FTC has become a little soft, not moving strongly enough to protect consumer interests, stop price-fixing or apply stringent antitrust standards to corporate merger proposals. Some of these complaints held up the commission's reauthorization in the past two years, although the last session's big sticking points were a push to require FTC regulation of certain professions and attempts to tack a legislative-veto measure onto the reauthorization.

Hill sources say those concerns still exist, but may not prove to be as big a barrier this time. Still, a source said, "there are a lot of other odds and ends that are controversial about the FTC to this group or that group."

This year, the source adds, "The real question is whether the commission is going to take any affirmative enforcement action in the areas that we consider to be their major mandate," including antitrust, consumer protection and price-fixing.

This can be tricky. Rep. James J. Florio (D-N.J.), chairman of the House Energy and Commerce subcommittee on commerce, transportation and tourism, the first hurdle an FTC reauthorization must clear, has said that it's easier to rein in an overzealous agency than it is to prod a lethargic one into action. Thus, said a congressional staffer, Congress may choose to try to exert some control over the FTC through appropriations bills, rather than through the reauthorization.

In any case, Miller said in his speech, "It's time to move FTC reauthorization now! . . . While the lack of congressional authorization may appear to be a technicality, I assure you that it can debilitate staff morale and impair the agency's effectiveness in protecting the public."