Misled by Central Intelligence Agency Director William J. Casey and encouraged by cheerleaders at the White House, President Reagan may be unwittingly squandering much of the good will he has established with the news media during the last 5 1/2 years.

Within the White House, officials delicately refer to the dusting off of a 1950 law, as a threat to prosecute news organizations that disclose communications intelligence, as "the Casey initiative." This is less than a warm embrace of Casey, who is seen as having a political need to deflect attention from recent espionage cases and particularly from the embarrassment caused by the CIA mishandling of KGB Col. Vitaly Yurchenko, who redefected to the Soviet Union last August.

Ironically, Casey's judgment also has been questioned from within because he agreed to Reagan's disclosure on national television, after the April 15 raid on Libya, that the United States has the ability to intercept and decode sensitive Libyan communications. The rationalization was that this disclosure was needed to demonstrate Libyan responsibility for the bombing of the West Berlin discotheque that was the excuse for the raid. Subsequent information suggests that Syrians may have had a hand in the bombing.

Reagan has always been naive about the nature of "leaks" in his rather porous administration. In the first term, he blamed the indiscretions of budget director David A. Stockman, the misjudgments of Environmental Protection Agency Administrator Anne M. Burford and the intramural battles of Secretary of State Alexander M. Haig Jr. almost solely on the news media.

While Reagan has made a career of celebrating the good sense of ordinary people and of mistrusting government, he believes that "news" about his administration should be based on the official version of events. Asked by me at a news conference June 30, 1982, to reveal the reasons for Haig's departure, the president replied, "If I thought that there was something involved in this that the American people needed to know, with regard to their own welfare, then I would be frank with the American people and tell them."

Nevertheless, Reagan was subjected in his first term to a healthy and vigorous exchange of differences on the merits of suppressing information in the name of national security. The most bitter battle was prompted by the reactions to a Sept. 12, 1983, report on NBC News and an account in The Washington Post the following morning that quoted unnamed White House officials as stating that Reagan had authorized Marines in Beirut to call in air strikes against forces shelling their positions in Lebanon. These officials told me that they wanted the story out because they believed that the Syrians would show restraint if they knew they might be bombed in retaliation for the deadly shellings.

The knowledge that information had been leaked to protect U.S. servicemen did not deter Casey, who joined with then-national security affairs adviser William P. Clark and then-White House counselor Edwin Meese III in persuading the president to investigate his own staff. This mischievous inquiry resulted in FBI interrogations of White House aides but produced nothing except a climate of fear. Reagan ultimately heeded the recommendations of then-chief of staff James A. Baker III and Secretary of State George P. Shultz and declined to authorize sweeping use of polygraph tests to find the culprits.

Now, Casey is again exaggerating the nature of the media threat, and there appears to be no White House official willing to do what Baker did three years ago. White House chief of staff Donald T. Regan is no media-basher, but he seems disinclined to risk the consequences of battling Casey, which caused Baker much grief.

The energy expended by the administration on the mindless investigation of itself in 1983 would have been put to better use in properly securing the Marine headquarters in Beirut. And that tragedy should be a reminder that national security is a concept that should be reserved for protecting secrets not known to the Soviets or other adversaries rather than a phrase to be invoked routinely in a contest with the news media.

Reaganism of the Week: Praising the "new spirit of enterprise" and the products that have resulted, the president said in a White House speech last Thursday that he had recently received an unusual gift. "It was a little duck," he said. "And if you squeezed it, it laid jelly beans."