President Reagan said yesterday that he believes the Soviets will be more willing to negotiate seriously on the removal of intermediate-range missiles in Europe as the date nears for deployment of U.S. Pershing and cruise missiles there.

"I think that there might be some loosening of the Soviet attitude as we get close to the day of deploying our intermediate-range missiles in Europe," the president said to a breakfast meeting of reporters in the White House. Site surveys for the U.S. missiles are under way in West Germany, Italy and Britain. Deployment is scheduled in December.

The United States has offered a "zero-option" proposal that the Soviets remove all their medium-range nuclear missiles in return for U.S. agreement not to deploy Pershing and cruise missiles. Yesterday one White House official said that "putting forth those principles does make it clear that we're willing to negotiate."

In a major foreign policy speech here Tuesday Reagan listed four "sound principles" for what could be an interim agreement allowing both sides fewer but an equal number of missiles in Europe. The principles include equality of forces, not counting British and French missiles, no shifting of Soviet missiles from Europe to Asia and a verifiable agreement.

Another White House official said yesterday that the administration was pursuing a policy that was "both hang-tough and flexible at the same time."

He said Reagan is, in effect, telling the Soviets that he would not abandon the zero option until there was a "serious" counterproposal while telling the allies that he would be willing to negotiate if this happened.

In response to another question, Reagan confirmed that a Soviet delegate had dropped "a hint" to chief U.S. arms control negotiator Paul H. Nitze that the Soviets "might look more kindly on cruise missiles than the Pershings. Again, I don't think cruise missiles alone would be a deterrent to the Soviet SS20s."

Reagan also said that a recent Soviet test of a new intercontinental missile "come the closest" to appearing to be a Soviet violation of the tacit observance by the two countries of the SALT II arms limitation treaty, which has never been ratified by the United States. He said "there have been hints" of other Soviet violations, but they have been impossible to prove.

On the Middle East the president was asked whether he had anything specific in mind when he said in his Tuesday foreign policy speech that the administration would take "all necessary measures" to guarantee Israel's northern border as part of any agreement for the withdrawal of Israeli and Syrian troops from Lebanon.

"This is not anything different than has been said before by me and by several presidents before me, that this country has always maintained that it has an obligation to the security of Israel," Reagan replied. But he spoke with intensity later in the breakfast as he contended that Israel has good reason to accept his Middle East peace plan, including a Palestinian entity on the West Bank.

"What is the stake for Israel?" the president said. "The stake is security. Can they go on forever living as an armed camp? Their economy's suffering. They have 130 percent inflation rate. And they're having to maintain a military presence that is out of all proportion to their size as a nation. And so the greatest security for Israel, and this is what's back of our Middle East peace plan, is to create new Egypts, more nations, more neighbors that are willing to sign peace treaties with them."

Later yesterday, Israeli Ambassador Moshe Arens, who will become his country's new defense minister, met for 15 minutes with Reagan and said afterward that the president "didn't go into much detail" about how he proposes to guarantee the security of Israel's northern border with Lebanon.

Questioned at yesterday's breakfast about his plans for 1984, Reagan joked that there was "a 50 percent chance" of his seeking reelection.

"I think to do it too early leaves you open to the charge that everything you try to do is based on politics," he added. "And if you say the other way too soon, why you're a lame duck prematurely. So I think it's a decision that I will come to and I will make at what I think is the appropriate time."