As expected, President Carter said yesterday that he will nominate Kurt W. Muellenberg, chief of the Justice Department's organized crime section, to be inspector general of the General Services Administration.

Muellenberg, 46, is known within Justice as a tough prosecutor and able administrator. His selection ends a power struggle that began when GSA Administrator Jay Solomon decided to push Securities and Exchange Commission attorney Irwin Borowski for the post, only to find that the White House supported neither Borowski nor Solomon.

If confirmed by the Senate, Muellenberg will become GSA's first inspector general at a time when the agency, which provides federal workers with office space and supplies, is the target of numerous criminal investigations across the country into fradulent contracting practices.

As inspector general, Muellenberg would be responsible for supervising GSA's internal investigations and audits. He also would be in charge of referring cases to the Department of Justice for possible prosecution.

The point at which such cases are referred has been a matter of contention between GSA and Justice, and the selection of Muellenberg, who has been with Justice since 1965, presumably will settle the argument and smoothe relations between the two agencies.

GSA has advocated investigating allegations thoroughly before turning cases over to Justice, while Justice has taken the position that prosecutors who may end up trying cases should supervise the investigations from their inception.

Muellenberg, who was born in Germany and came to this country in 1952, has held various positions in the organized crime field at Justice, including chief of the Cleveland organized crime strike force and deputy chief of the Detroit strike force.

"He's tenacious, and he doesn't give in on policy matters," a colleague said of Muellenberg this week "He's a straight-shooting, tough prosecutor," another said.