Secretary of State George P. Shultz said last night that the use of covert measures to combat terrorism has become "imperative" and pledged the administration to use such means "legally, properly and with the due involvement" of congressional oversight committees.

"What is crucial is the ability to take some initiatives quietly, in situations where the more the measures are known, the less effective will be their results," the secretary said in a dinner speech to the American Jewish Committee here in which he also appealed for greater allied unity in the war against terrorism.

"We have to get over the idea that 'covert' is a dirty word," Shultz said, a theme he has emphasized with increasing frequency in the past few months. Some U.S. officials suggested that Shultz may be preparing the public for the future use of covert measures to strike against known terrorists and their bases.

"Free nations accustomed to open debate are naturally uneasy about covert measures, just as they are uneasy about the ambiguous circumstances that require us to act in secret," Shultz said. "Yet we must remember that intelligence breakthroughs and secret operations had a decisive influence on our victories in two world wars."

"Today, in our shadow war against terrorism, the use of these instruments is just as imperative," he added.

Apparently seeking to allay public fears that any resort to covert methods might go awry, Shultz promised that the administration "will use such measures legally, properly and with the due involvement of designated legislative committees."

This appeared to be a reference to the House and Senate intelligence committees, which are supposed to be informed in advance of any covert actions.

Shultz told his audience that Western nations, working in closer cooperation, now hold "the winning hand" in their battle against terrorism. "We have to keep this momentum going," he said.

The secretary acknowledged that last month's air strike against Libya, which resulted in the death of Libyan leader Muammar Qaddafi's adopted daughter and other civilians, generated criticism and "less public consensus" abroad than the administration would have liked. But he said the results are now "convincing the skeptics."

"Qaddafi is in retreat and Syria is uneasy," he said, adding that he hoped the Syrian unease "may induce that country to think hard about involvement in murderous adventures."

Syria has been implicated by Israeli and British authorities in an attempt to place a bomb aboard an Israeli El Al flight bound for Tel Aviv. Deputy Secretary of State John C. Whitehead said Tuesday the administration had "no reason to doubt" Israeli government information tying Syria to the El Al incident and to the April 5 bombing of a West Berlin club in which a U.S. soldier and a Turkish woman were killed.

Shultz also voiced a strong plea for the administration's proposed $354 million sale of 2,600 air-to-air and ground-to-air missiles to Saudi Arabia. The proposal has already been turned down by more than two-thirds of both houses of Congress, enough to override an expected presidential veto. The White House is campaigning to save the arms sale.

Shultz said that Islamic fundamentalism in Iran posed a real danger and that if it swept into Saudi Arabia, "America's strategic interests will be harmed, and needless to say, so will Israel."

"There are many in the Arab world who want peace and stability and moderation and who can be brought to accept the permanent reality of the state of Israel," the secretary said.

"But if America cannot demonstrate that we are a constant, effective, strong and responsive presence in the Middle East, those with the best of inclinations inevitably will make their accommodation with those who bear the worst intentions toward us."

Shultz appeared to be suggesting that Saudi Arabia and such moderate Arab states as Jordan might eventually align themselves more closely with Libya and Syria if the proposed arms sale is defeated.