Republican members of the Senate Commerce Committee yesterday charged the Reagan administration with ignoring antitrust enforcement, with one member asking that the nomination of James C. Miller III to chair the Federal Trade Commission be held up as a result.

"The Reagan administratio;n, in my view, has demonstrated a singular lack of interest in the enforcement of antitrust laws," said Sen. John Danforth (R-Mo.) during Miller's confirmation hearings. "This, in my opinion, is a mistake."

"Free and open competition is at the heart of Republican philosophy, and diligent enforcement of the antitrust laws is important to the maintenance of a competitive marketplace," Danforth said.

"Conglomerte mergers and vertical practices may not necessarily stifle competition -- but they can, as Mr. Miller hs acknowledged. The role and function of the FTC is to act as a watchdog of our economic system."

Danforth, Sen. Robert Packwood (R-Ore.), the committee's chairman, and Sen. Slade Gorton (R-Wash.) emphasized that any changed in antitrust policy would have to be made by Congress and not by Miller at the FTC. Miller suggested to the commitee last week that he would review the FTC's antitrust activities and called some FTC actions "misdirected." t

Gorton called signals from the administration, such as the Justice Department's willingness to drop its antitrust suit against American Telephone & Telegraph Co. in exchange for communications legislation, evidence of "indifference about the enforcement of antitrust laws."

Although the committee approved the nomination by a 16-to-1 vote, with Gorton the lone dissenter, Gorton immediately wrote to Senate Majority Leader Howard Baker (R-Tenn.) asking Baker to hold up the nomination.

Expressing serious reservations about administration actions on the AT&T case and the Conoco Inc. takeover situation, Gorton asked that the hold apply "until I have had an opportunity to discuss these matters" with Miller and administration representatives. Committee aides said that Gorton's request was almost certain to be honored by Baker.

Meanwhile, the Justice Department was sending out a new set of signals, asking Mobil Corp. for additional information about its proposed takeover of Conoco, a move that delays Mobil's ability to acquire Conoco stock for 10 days past Mobil's response to the government's request. Simultaneously, a top Justice Department antitrust official wa denying that the government was in the process of dramatically changing federal antitrust policy.

"Our own view is that the changes likely to occur will differ only incrementally -- not radically -- from the policies of our predecessors," said Abbott B. Lipsky Jr., deputy assistant attorney general in the antitrust division, in a speech here.

"My prupose is to remind you that despite the arguments -- over merger policy, for example -- there remains agreement that the most fundamental purpose of the antitrust laws, the prevention of private cartel activity, is still endorses without reservation by this administration, and that this prupose is still strongly supported from nearly every point of thepolitical compass," Lipsky said.

Lipsky also said the administration is committed to jailing pricefixers, and companies and individuals engaging in cartel-like behavior.