U.S. District Judge Harold Greene yesterday delayed the opening of the Justice Department's landmark antitrust suit against American Telephone & Telegraph Co. from late October until January, but sharply criticized the government for asking that both sides abandon the complex stipulation process laying out the premises of the case.

The government made its position known in a memo filed with the U.S. District Court here Thursday as the two sides prepared to go before Judge Greene to consider the calendar for the case.

"I regard that suggestion as irresponsible," Greene said of the government proposal. Greene also said that the government's objections to continuing the talks between lawyers from AT&T and the government were "exaggerated in a number of respects."

Greene, who repeatedly cited the three-year duration of the government's case against International Business Matchines Corp., called on the governmnet to allocate the necessary resources to move the case quickly and said the parties are the "largest and wealthiest litigants in the world."

Assistant Attorney General Sanford Litvack, who attended the hearing, said the "government is a big government" and would "make available" whatever resources the trying of the massive case requires.

At the close of the session, Greene said he would issue an order next week as to the handling of the pretrial talks and suggested the trial would start in early January.

"After careful consideration" the Justice Department concluded the stipulation process would delay the trial well into next year and "should therefore be terminated," wrote the government team, headed by Gerald Connell.

The government considers the six-year-old case among the most important antitrust suits ever filed, and is asking for a breakup of AT&T, charging AT&T, the nation's largest company with violating antitrust laws in in monopolizing the communications industry.

The novel stipulation process was designed in part to avoid the quagmire in which the government finds itself in the 10-year-old antitrust case against IBM and is an effort to lay out carefully the basic charges in the case before the trial opens.

On the other hand, AT&T said in a memo also filed Thursday that the stipulation process "is achieving substantial results and continues to possess the potential to become a model of the judicial administration of massive, complicated litigation."

In the filing, AT&T attorneys asked Greene to permit the process to continue, even though negotiations have been completed for only 11 percent of the pages under consideratin since the stipulation talks began in April.

"Whether out of a desire to blur the fundamental issues in the case or simply a desire to devote its resources to activities it believes should have a higher priority, the government has evinced steadily declining optimism for the results achieved by the negotiations," AT&T attorneys wrote.

In a filing last week, AT&T said the stipulation talks could be completed within three and a half months, although the government charged that "virtually no facts were put forward" to support the estimate. But the Justice Department also said that the estimate does not include time needed to take depositions from 450 witnesses listed by Bell System lawyers.

"It is for this reason that we recommend the stipulation negotiations not be continued beyond Sept. 15," wrote the government team, headed by Gerald Connell.

But at the same time the government lawyers said that AT&T attorneys have stated that if the stipulation talks are cut off, AT&T might call as many as 900 witnesses. If the trial is to begin in January, the government said Greene would have to revise his stand barring the taking of depositions of AT&T witnesses after the trial begins.