The Federal Trade Commission, acknowledging that it has been guilty of "harmful" and "unnecessary" delays that have allowed some cases to drag on for years before reaching decisions, yesterday adopted a series of rule changes aimed at streamlining its procedures.

The changes--which come on the heels of increasing criticism from Capitol Hill--will, for the first time, set specific timetables for voting, establish "target dates" for issuing opinions, and give broader authority to bureau directors to close out unproductive investigations.

While most of the changes were unanimously adopted, the commissioners--who have been deeply split along ideological lines for the past two years--quickly disagreed as to whether they will get to the root of the problem.

One of the commissioners, former chairman Michael Pertschuk, charged later that at least some of the delays have been deliberately engineered by chairman James C. Miller to stall until a Reagan administration majority takes hold at the agency. This is now imminent, in light of this week's presidential announcement of the impending nomination of conservative law professor Terry Calvani.

"You have chronic delays at the commission and that's nothing new," said Pertschuk. "But then you have other delays that are not all that accidental. It's hard not to conclude there isn't a pattern here."

Miller sharply disputed Pertschuk's charges, saying that the delays he caused were due to the shoddy work being done by the commission before he took over in October 1981. "They were engaging in knee-jerk law enforcement," Miller said, and many investigations were "absolute disasters."

Among the delays cited by Pertschuk are a number of the cases in which FTC staff recommended actions to bureau directors without those recommendations ever being forwarded to the full commission. In one case, FTC staffers reached a consent agreement with the Viking Sewing Maching Co. of Minneapolis to refrain from resale price maintenance--a form of price-fixing in which a wholesaler dictates the price that a retailer must charge for his product--on July 28, 1981. In March of this year, 20 months later, the agreement was returned by Miller to the staff for more analysis; it has still not reached the commission for approval.

In another case, a staff investigation of defective paint used by a European auto company resulted in an informal consent agreement with the commission staff in May of 1982. The Bureau of Consumer Protection didn't approve the agreement until July of this year, by which time the company indicated that it may no longer be willing to go along with it.

Replied Miller, "Consent agreements are negotiated by the staff--and just because something is negotiated doesn't mean its good or bad."