The special prosecutor investigating allegations of cocaine use against former White House aide Timothy Kraft has suspended his grand jury inquiry in New Orleans while he fights a challenge to the constitutionality of his mandate.

Gerald J. Gallinghouse, former U.S. attorney in New Orleans, was appointed in September to investigate the charges against Kraft under the special prosecutor provisions of the 1978 Ehtics in Government Act. Last month, Kraft's attorneys, A. Raymond Randolph and Thomas Green, filed a suit claiming that the act is unconstitutional.

In a Dec. 12 letter to U.S. District Court Judge Barrington D. Parker, Gallinghouse said he suspended the investigation "during the pendency of this proceeding." He said he had asked Deputy Attorney General Charles B. Renfrew to have the Justice Department represent him in the case and was referred to a Civil Division attorney. Later, however, he said he was told that Attorney General Benjamin R. Civiletti had rejected the idea as inappropriate, "presumably because of the independence of the special prosecutor from the Department of Justice."

Gallinghouse asked Parker to give him until Jan. 15 to respond to the suit because he will have to find outside counsel to represent him.