Two seats are opening up on the five-member Federal Trade Commission, but no one thinks the changing roll call will shift the agency's direction from the conservative course set by outgoing Chairman James C. Miller III.

Senate sources expect Miller to be easily confirmed to replace David A. Stockman as director of the Office of Management and Budget, where Miller served in the early days of the Reagan administration. Miller's friend, coauthor and ideological soulmate, Commissioner George W. Douglas, said months ago that he plans to leave the commission by Sept. 1.

Those two openings create a number of possible personnel shifts, but most are in the rumor stage.

Some congressional and staff sources say they think that Miller will urge Douglas to stay on to replace him as FTC chairman. A conservative economist and active proponent of deregulation, Douglas would be Miller's logical heir, except for one small problem: Douglas is a Democrat.

Most observers think that it is unlikely that President Reagan would appoint a Democrat as chairman, even a conservative like Douglas. But then again, Reagan has always said he welcomes converts to the Republican party.

Whatever Douglas decides, the three FTC bureau directors are all considered to be candidates for a commission seat:

*Carol T. Crawford served as Miller's executive assistant from October 1981 until becoming director of the FTC's Bureau of Consumer Protection in April 1983. An attorney, Crawford served as a legislative assistant to Sen. Bob Packwood (R-Ore.), and as a senior adviser to the Reagan/Bush transition team for the FTC.

*Wendy Lee Gramm, director of the Bureau of Economics since March 1983, is an economist on leave of absence from the faculty of Texas A&M University. Before becoming bureau director, she worked for a year as the bureau's assistant director for consumer protection. She is married to Sen. Phil Gramm (R-Tex.).

*Timothy J. Muris, head of the antitrust bureau, came to the FTC with Miller from OMB. Some considered him to be Miller's right-hand man. Others go farther and say he was the real architect behind Miller's efforts to implement the Reagan philosophy at FTC. Muris was director of the Bureau of Consumer Protection from October 1981 until becoming director of the Bureau of Competition. He served as a deputy counsel to the presidential Task Force on Regulatory Relief and was a member of the Reagan/Bush transition team for the FTC.

Only one of the bureau directors could be promoted because they are all Republicans. According to commission rules, only three of the five seats may be held by members of any one party, and two are now held by Republicans Patricia P. Bailey and Terry Calvani.

Also keeping people guessing is the FTC's director of congressional relations, Karen Johnston, who also had worked for Miller at OMB. Johnston has always said she will stay on at least through the FTC reauthorization struggle. The Senate approved an FTC reauthorization bill last month. The House bill is pending before the Rules Committee.

Miller has said he will not make any job offers until after his confirmation.

PENALTIES SOUGHT . . . The watchdog newsletter FTC Watch reported that the FTC is asking the Justice Department to seek millions of dollars in civil penalties against American Hospital Supply Corp. for alleged multiple violations of a 1981 consent agreement.

Neither the company, the FTC, nor the Justice Department would comment on the story. But FTC Watch said the company contends the violations, if they occurred, were inadvertent and were brought to the FTC's attention by AHS' counsel.