The day before his Watergate pardon was announced, Richard M. Nixon telephoned President Ford and threatened that unless it was granted he would claim publicly that Ford "had promised the pardon in exchange for the presidency," according to an article in Atlantic magazine.

The alleged phone call was made Sept. 7, 1974, as a lawyer representing Ford was in San Clemente, Calif., negotiating with Nixon and his representatives on conditions under which a pardon would be granted, according to the report by Seymour M. Hersh.

"Nixon's message," Hersh writes, "was blunt, according to those few White House aides who knew of the private call: if Ford did not grant him a full pardon, he, Nixon, was going to go public and claim that Ford had promised the pardon in exchange for the presidency, because Ford was so eager to get it."

Hersh's 20,000-word article in the magazine's August issue examines events surrounding Nixon's resignation as president Aug. 9, 1974, Ford's pardon of Nixon Sept. 8 and the role played in both events by then-White House chief of staff Alexander M. Haig Jr., a holdover from the Nixon White House.

The article is certain to revive speculation that Nixon, in return for the promise of a pardon, struck a deal with Ford through Haig to resign the presidency rather than face impeachment for Watergate-related offenses.

Ford repeatedly has denied making any such bargain before Nixon's resignation. Hersh writes that Ford, in an interview with him in April, "emphatically denied" making such a deal with Haig during a private meeting eight days before Nixon resigned.

"Many of the aides who worked closely with Haig and Ford still assume that there was a deal of some kind," writes Hersh, who stops short of making such an assertion. "Whether there was a deal may never be known, because the men involved have yet to give a full account," he writes.

None of the aides who knew of Nixon's alleged call to Ford the day before the pardon is identified. Hersh writes that, in the April interview, Ford denied any recollection of such a call. Ford told Hersh, according to the article, that White House logs for Sept. 7, 1974, show no phone call from Nixon to Ford.

Although Hersh writes that a "Ford associate" said Ford's denial of the phone call was not categorical, Robert Barrett, a spokesman for Ford, said last night that Ford's response to Hersh's question was intended to convey a flat denial.

Although much of Hersh's article is based on previous reports and memoirs of participants, he provides some new details concerning Nixon's last days in office and the pardon. These include:

* Haig instructed Ford's secretary to falsify the log of an Aug. 1 meeting between them, leading to the inference, Hersh writes, "that whatever was to take place in the meeting with Ford--in Haig's mind, at least--would not stand up to public scrutiny." Hersh says Haig did not respond to requests to explain his action, and Haig could not be reached for comment yesterday.

* Then-Defense Secretary James R. Schlesinger Jr., concerned that Nixon might make a desperate attempt to stay in office by using troops, sounded out the Joint Chiefs of Staff to determine how they would respond to an extra-constitutional effort by the president.

Schlesinger reportedly was worried that Nixon, who had close ties with Marine Commandant Robert E. Cushman Jr., might call upon Marines in the Washington area, although Hersh never says how the Marines might have been used.

"Schlesinger began to investigate what forces could be assembled at his order as a counterweight to the Marines, if Nixon--in a crisis--chose to subvert the Constitution," Hersh reports.

Weeks after Nixon resigned, it was reported that Schlesinger had clamped tight controls on the military, instructing that no orders to the military outside the chain of command were to be followed.

* Leon Jaworski, who resigned after serving 50 weeks as Watergate special prosecutor, may have done so to avoid a tax problem he would have faced had he stayed a full year.

Hersh, a former New York Times reporter, is author of "The Price of Power," about Henry A. Kissinger's tenure as national security affairs adviser and secretary of state under Nixon and Ford.