The Justice Department yesterday rested its massive antitrust suit seeking to break up the American Telephone & Telegraph Co. and began the wait for counter-attacks by AT&T and perhaps, the White House.

After introducing a final group of documents, the department's chief trial attorney Jerry Connell brought the government's case to a close, following 61 days of testimony by 93 witnesses.

U.S. District Judge Harold Greene praised both sides for moving the trial so smoothly through its first phase. To Connell, he said: "Without indicating anything at all about the merits, you did manage in four months to properly present your side of the case."

Connell told reporters that he was "very pleased" with the government's case, which accuses AT&T of conspiring to eliminate or frustrate competition in the markets for telecommunications equipment and intercity phone service.

George Saunders, AT&T's lead attorney, said he too thought the government had told its story well. "They gave an opportunity for anyone who has a complaint against the Bell System to testify," he said. "I don't think they've told a new story. . . . I think the story is a weak one," Saunders added.

Saunders said the company was ready to begin its defense on Monday by calling Dr. Ian Ross, President of Bell Laboratories, AT&T's research arm, the first of an expected 350 to 450 defense witnesses.

Both Saunders and Connell said they expect the trial to proceed to its conclusion late this year and had no idea where the Reagan administration stands on the case, which had divided some of President Reagan's chief cabinet advisers.

A special cabinet-level task force has recommended that the government abandon the case on grounds that it is disrupting the telecommunications industry at a time when foreign competition is becoming a serious threat, according to administration officials. Commerce Secretary Malcolm Baldrige has said publicly that he disagrees with the Justice Department's plan to break up AT&T, and Defense Secretary Caspar Weinberger is arguing that AT&T's communications network is too important to the national security to be subjected to antitrust prosecution.

But that thrust was reportedly stalled, at least for a time, following a reportedly inconclusive review of the issue by Reagan and cabinet officials two weeks ago. Instead, Assistant Attorney General William Baxter, head of the antitrust division, was asked to suggest a legislative plan for dividing AT&T into smaller pieces that would satisfy the Justice Department, officials said.

Justice Department spokesman Tom DeCair said yesterday he believes that no final decisions have been made on the telecommunications issues.

Despite the tremendous stakes in the case, it has been a model of courtroom brevity and geniality, both sides agreed, in sharp contrast with the Justice Department's much longer and contentious antitrust suit against International Business Machines Corp.

Judge Greene took part in some banter yesterday about the volleyball contests between Justice and AT&T trial teams at a joint picnic last week. "I've gotten some publicity about being athletic at the volley ball game that will surprise my friends no end," said the judge.

The bantering continued at the close of yesterday's session. Asked by reporters to cite some highlights of the government's case, Connell mentioned a surprise witness from a small AT&T competitor, Telesciences Corp., which was unsuccessful in selling its telephone monitoring equipment to Bell affiliates despite its superior quality compared with Bell's Western Electric equipment, according to the witness. Justice hopes to prove an anticompetitive relationship between Western Electric and the Bell System telephone companies to support a break-up of the world's largest corporation.

"Don't get too far out on that limb, Jerry," Saunders told him.

"We're getting ready to saw it off."