The Federal Communications Commission yesterday delayed for at least five months a major restructuring of American Telephone & Telegraph Company's Wide Area Telecommunications Service (WATS) rates, a proposal that would have raised charges by about 50 percent for many of the nation's largest companies.

The commission, without dissenting votes, ordered a staff investigation of the rate charges in light of the Bell Sytem's failure to encourage time-of-day or off-peak-hour pricing systems.

AT&T filed the rate revision three months ago and said the new, complex rate scheme would be largely based on usage and actually would cut the rates for about 90 percent of the approximately 100,000 users of the service.

WATS enables customers to place long-distance calls for a set rate and also permits consumers to place long-distance calls to businesses using an "800" number. Many of those large firms had joined to fight the rate increases.

Simultaneously, U.S. District Judge Harold Greene reiterated yesterday that the Justice Department's landmark antitrust case against AT&T would open on Jan. 15, despite a flap between the phone company and the government over the stipulation process in the case.

Greene had set up these talks in the case to lay out the charges and evidence in the six-year-old case to simplify the suit and avoid the lengthy trials of other major antitrust cases.

"I'm going to be here on the 15th of January," Greene told lawyers for AT&T and the Justice Department during a pretrial hearing. "We're going to go to trial that day." Greene said he is likely to issue a ruling on the problems with the negotiations next week.

The generally secret stipulation process has been ensnarled in a controversy about a decision by the special masters in the case, the supervisors of the unique stipulation process, who ruled on Nov. 26 that no evidence could be presented in the case unless those facts are linked to specific contentions by the government.

The government's chief prosecutor in the case, Gerald Connell, refused to sign any further stipulations in the case until a definitive ruling from Greene was made on the masters' order. Connell told Greene yesterday that the stipulation ruling "really changes the basic ground rules" of the process.

Connell also changed that AT&T attorneys are "litigating the process using technicalities to prevent" the government from making its case and said the government's trial team was not "trying to shut down the process."

George Saunders, the lead AT&T attorney, said "there is no excuse for what they [the government] has done" and contended that the Justice Department has "virtually gutted the stipulation process," leaving it "nearly in shambles."