President Reagan announced a "measure of agreement" yesterday with leaders of the Senate Select Committee on Intelligence on procedures involving covert operations, but informed sources said there is still disagreement over deadlines for reporting certain covert actions to Congress.

Chairman David L. Boren (D-Okla.) and Vice Chairman William S. Cohen (R-Maine) appeared with the president at a White House picture-taking session. Reagan handed them a letter responding to their suggestions July 1 about changing procedures for reporting and approving covert operations in the aftermath of the Iran-contra affair.

The letter was part of a White House bid to repair the damage of the Iran-contra scandal, and Reagan is to continue the effort Wednesday with a nationally televised speech.

However, the letter also highlighted differences between Reagan and Congress over the president's authority to approve covert operations.

The Iran-contra congressional hearings have disclosed that Reagan approved clandestine arms sales to Iran, then withheld details of the secret operations for at least 16 months under a provision of the law requiring "timely notification" to Congress.

That provision is supposed to be used in cases where Congress cannot be given prior notice. Many members of Congress have said Reagan may have violated the law by failing to notify Congress until after the arms sales became public last November.

The Iran-contra hearings also showed that Reagan's subordinates created after-the-fact presidential intelligence "findings" to justify covert operations, and former national security adviser Rear Adm. John M. Poindexter testified that he destroyed one finding to save Reagan from political embarrassment.

Yesterday, in his appearance with Boren and Cohen, Reagan emphasized the "spirit of bipartisan cooperation and agreement about procedures governing . . . sensitive intelligence activities." Boren saidthat Reagan had taken a "good first step toward cooperation" and that the procedures were a "marked improvement."

However, most of the procedures to which Reagan agreed in his letter were put in place after the report of the Tower commission last spring, a White House official said.

Administration and congressional sources said differences remain over some procedures. Reagan promised "maximum consultation and notification" of covert actions to Congress but said he "must retain the flexibility as commander in chief and chief executive to excercise those constitutional authorities necessary to safeguard the nation and its citizens . . . . "

The president did not elaborate on this point, but it drew objections from Rep. Louis Stokes (D-Ohio), chairman of the House Permanent Select Committee on Intelligence.

Stokes said he "can't accept the president's assertion that he possesses inherent constitutional power" to bypass congressional-notification requirements.

Boren said he will await an executive order that Reagan has directed his staff to prepare before making a judgment on yesterday's letter.

Asked whether he was announcing the changes because of the mistakes of the Iran-contra affair, Reagan said, "I haven't called them mistakes yet." However, in a radio speech last Dec. 6, he said that "mistakes were made" in carrying out his Iran policy.

The president, who has held only two news conferences this year and plans none until fall, refused to answer questions yesterday about the new intelligence procedures or developments in Central America.

He also refused to answer questions when appearing before reporters earlier in the day to announce new unemployment statistics. He told them to "tune in" to his speech Wednesday night.

In his letter to the senators, Reagan promised to make his covert-action "findings" in writing "except in cases of extreme emergency" and said that, if an oral directive is necessary a contemporaneous record would be made, reduced to writing and signed by the president as soon as possible.

Reagan also promised not to make retroactive findings, as he had signed during the Iran arms sales; to tell Congress of the involvement of agencies and persons outside the Central Intelligence Agency; to identify third countries and private parties involved in covert operations, and to continue the "regular and periodic review" of covert operations by the intelligence committees and the National Security Council.

The senators urged Reagan to make a commitment to notifying Congress "in all cases without exception" at the time a covert operation begins if he could not notify Congress in advance and to do so "in no event later than within 48 hours."

However, Reagan said he would not delay notification beyond "two working days" in "all but the most exceptional circumstances." This appeared to give the president leeway to delay telling Congress for more than two days in cases determined to involve "exceptional circumstances."Staff writers Helen Dewar and Walter Pincus contributed to this report. Nose Surgery 'Successful,' Presidential Doctors Say Associated Press

President Reagan's doctors say his skin cancer surgery was "completely successful" and that they have removed all stitches from the tip of his nose, his spokesman announced yesterday.

A seven-doctor team cut a nearly half-inch basal cell carcinoma from Reagan's nose July 31 at Bethesda Naval Hospital. For the last week, the president has sported small bandages, covering 20 stitches.

Spokesman Marlin Fitzwater said Reagan's physician, Col. John Hutton, accompanied by three colleagues visited Reagan at the White House residence Thursday evening.

"After thorough examination, the sutures were removed," Fitzwater said. "The operation has been completely successful."