President Reagan was holding a copy of the daily White House news summary last Tuesday afternoon, scanning the reports of editorial commentary about the worst stock market dive in history, when his senior economic advisers arrived for an emergency meeting.

Treasury Secretary James A. Baker III, Federal Reserve Board Chairman Alan Greenspan and chief of staff Howard H. Baker Jr. had an urgent mission, but first they listened as Reagan reviewed the editorial opinions, summarized on the last page of the news summary.

The Chicago Tribune, for example, urged quick action to reduce the budget and trade deficits. But Reagan focused approvingly on The Wall Street Journal editorial of Monday morning titled "Time to Stand Tight." The editorial said Reagan's policies had created a five-year bull market and "the dramatic fall in stocks is all the more reason to stand tight: no tax increases, no protectionism . . . . "

Within two hours after he cited those words privately in the White House residential quarters, Reagan had been persuaded to go the opposite route, reading a statement to reporters outside in which he all but abandoned his longstanding opposition to tax increases and agreed to open new budget negotiations with Congress.

This scenario was a climactic moment in one of the gloomiest weeks of the Reagan presidency. From conflict in the Persian Gulf to the stock market plunge, from faltering arms-control negotiations to the final defeat of Robert H. Bork's nomination to the Supreme Court, Reagan was tossed by events beyond his control.

The events of last week underscored Reagan's waning power over the international and domestic agendas. Some White House officials were relieved that the president was forced to cancel a private meeting Tuesday with the Republican presidential candidates because of the likelihood that all six would be distancing themselves from him afterward in public, further advertising his weakened position. Even Vice President Bush, who has made loyalty a trademark of his service, was no longer standing by Reagan at week's end. Bush announced that a tax increase should not be considered in the wake of the stock market crisis.

Despite the setbacks, White House officials said yesterday they are looking for ways to recover this week. "By the end of the week a lot of things can happen," including a possible "framework" for compromise on the budget and announcement of a new Supreme Court nominee, one senior White House official said. Reagan is also expected to take an upbeat approach to arms control in his Wednesday address at West Point. In addition, the officials said Reagan had been distracted and worried about the health of First Lady Nancy Reagan before her mastectomy Oct. 17 to remove a cancerous tumor, but he has been more focused on official business since her successful operation.

He had plenty to focus on. The administration has increasingly found itself thrown on the defensive; last week it was repeatedly victimized by events it did not foresee and to which it had trouble reacting.

For weeks, the president's top advisers had expressed confidence that Secretary of State George P. Shultz would return from Moscow with a date for the summit in the United States with Soviet leader Mikhail Gorbachev. The president's calendar has been kept open for November in anticipation of a Thanksgiving summit to sign his first major arms-control agreement and for Gorbachev to tour the United States. As late as Thursday evening, Reagan talked happily about showing Gorbachev "things that he couldn't accuse us of staging" for him, including the Reagans' California ranch house where Gorbachev could "see how a capitalist spends his holidays."

"I want it to take place very much," Reagan said. But a senior White House official acknowledged the next day, after Shultz reported there would be no summit date: "We built expectations too high."

In the Persian Gulf, too, the administration struggled to react to events. The reflagging of Kuwaiti ships, which began in an effort to restore American power and prestige in the region after the humiliating Iran-contra affair, quickly has evolved into a precarious tit-for-tat in which Iran's Ayatollah Ruhollah Khomeini chooses the targets and the United States decides whether to respond.

Iran has now launched three Chinese-made Silkworm missiles at Kuwaiti targets. "We're going to try to point out to him that it's a little too expensive to keep that up," Reagan said last week. But his remark echoed the warnings made in vain at the June economic summit when Iran had not yet deployed the Silkworms and the administration hinted at a preemptive strike against them.

"If they do deploy them, we have a very serious situation on our hands," chief of staff Baker said of the Silkworm missiles then. "Once it's installed and erected on its platform, ready for launching, you have only seconds notice before it in fact can begin its flight toward naval vessels in the Persian Gulf. So that's a bad problem for us. You know, you almost can't wait until the missile is in flight before you begin to protect yourself, because there's such a short interval."

When the missiles did begin flying, Reagan chose to retaliate not against the missile sites but against a former oil drilling platform used for guiding Iranian gunboats. The administration called the reponse "measured and appropriate."

Coming amidst these difficulties, the Bork rejection had been expected for some time. But the 58-to-42 Senate defeat, widest margin of defeat for any Supreme Court nominee in history, was still a reminder of the internal ideological warfare that has gripped the administration. For all the attention focused on the campaign against Bork by his opposition, White House officials have acknowledged the administration underestimated the intensity of the opposition and failed to counter it with a strong, aggressive case for the nominee.

The stock market plunge jolted Reagan into negotiations on the budget, but, by all accounts, it was an agonizing process. He was hesitant and reluctant to invite compromise when the two Bakers and Greenspan, among others, came to him on Tuesday, and he wanted to "stand tight," as The Journal editorial suggested.

The one argument that was most persuasive in Reagan's decision to authorize the negotiations was that his entire legacy was at stake, officials said. Reagan was also warned that without action there was the specter of uncontrolled panic by consumers and international markets that could cause immediate and genuine damage to the economy, White House officials said.

While approving new budget negotiations, Reagan appeared to be at war with himself over the wisdom of it. After his news conference Thursday night produced simultaneous attacks on Congress and offers of compromise, one long-time Reagan adviser remarked, "There was the part for him, to make him feel better. And there was the part for the rest of us."

A well-informed Wall Steet analyst who favors a large, multiyear deficit-reduction package said Reagan may have bought time last week but the most difficult challenge is to prevent a cosmetic outcome that could lead to another market collapse. "The guys in Washington deserve a tremendous amount of credit for bringing the president along," he said, "but it's got to be a multistep process. They are going to have to nurse him along through the whole negotiation, making sure it produces more than just a joke."