President Carter sharply accelerated the pace of his talks with Israel's Menachem Begin and Egypt's Anwar Sadat at Camp David yesterday in a varied pattern of meetings that suggested intensive negotiations on a Middle East peace settlement have begun.

The three leaders met without aides in two separate sessions that consumed more than five hours of the second full day of contacts at the presidential retreat. Officials of the three delegations continued to refuse to give any details of the talks or to characterize them in any way.

But the day's schedule of meetings hinted that Carter's foreign policy advisers were concentrating their attention on Israeli negotiating positions, which Carter has identified in the past as insufficiently flexible, and particularly on Israel's concerns about security.

Defense Secretary Harold Brown traveled to Camp David from Washington in the afternoon to join Secretary of State Cyrus R. Vance and Carter's national security affairs adviser, Zbigniew Brzezinski, in a one-hour meeting with Israeli Foreign Minister Moshe Dayan and Defense Minister Ezer Weizman.

Vice President Mondale also arrived from Washington, to attend part of that session. Carter had started the day by meeting with Begin for two hours in the presence of their principal advisers, who continued talking for 80 minutes longer after Carter and Begin broke off to begin their private morning talk with Sadat.

The three leaders met for three hours before breaking to lunch separately, and then resumed their talks at 5 p.m.

While White House press secretary Jody Powell sought to dampen all speculation about the pattern of meetings and Brown's arrival, he said at another point, in response to a question, that he "wouldn't be surprised" if the discussions yesterday had dealt with the main deadlock in the Egyptian-Israeli peace negotiations, Israeli occupation of the West Bank territory of the Jordan River and the Gaza Strip.

While the U.S. delegation appeared to be acting as a catalyst in terms of scheduling talks, Powell described the president's role at this point in passive terms, saying that Carter "is spending a great part of his time listening" to the other parties.

Brown "is not here because of a particular development within the discussions at all," Powell said, adding that the defense secretary will join the administration's regular Friday morning foreign policy breakfast meeting, which will be held today at Camp David.

No significant details of the talks, which Powell said would probably continue at least through the weekend, filtered through the tight screen of secrecy that Carter has imposed on the summit meeting. But informed sources reported that the two foreign leaders both appeared to be in good spirits after the lengthy morning session, which ran twice as long as did the opening trilateral meeting on Wednesday.

Another apparent sign of a favorable atmosphere was a 25-minute meeting between Sadat and Weizman on Wednesday afternoon. The Egyptian president and the Israeli defense minister developed a strong personal attachment during a series of previous meetings and Sadat extended an invitation to Weizman to meet at his lodge. The two men were accompanied by aides, informed sources said.

Prior to the summit, reports circulated suggesting that Carter might propose an American Guarantee of Israel's security, including the possible presence of American military forces in the region, in the hope of persuading Begin to agree in principle to an Israeli withdrawal from the West Bank and the Gaza Strip.

During his vacation in Wyoming, the president was asked about the reports and did not rule out proposing an American role in a peace settlement. But yesterday, Powell used words like "hogwash" when asked about some of the reports and their possible connection with Brown's arrival at the summit.

"The question was what about American troops in the Middle East," he said to several hundred reporters crowded into an American Legion hall here for his daily briefing.

"That is one of the great nonexistent stories of all time that run and rumbled and ricocheted around the world for a couple of days based on entirely nothing except, I understand, a chance comment made by way of example in front of some American congressmen . . ."

With so much at stake politically for the three leaders, it was never anticipated that the summit would end abruptly after only a day or two. Those expectations seemed borne out by yesterday's developments and Powell's comments.

Powell said that today, tomorrow and Sunday there will be "breaks" in the discussions for Arab, Jewish and Christian religious services respectively, but that contacts among the delegations would continue. He said the religious services will be held inside Camp David and that there are no plans for any of the three leaders to leave the presidential compound.

Begin has always refused to conduct business on Saturdays, the Jewish sabbath, but other members are of the Israeli delegation are less orthodox in their religious observances. Saturday would also provide time for discussions between Carter and Sadat.

Last night, reporters who are covering the summit conference from the press center here six miles west of Camp David got their first view of Carter, Begin and Sadat in more than 48 hours. Reporters were allowed into a corner of the Camp David grounds to see the three leaders watching the traditional evening dress parade by Marines from the Marine barracks in Washington.

Following the parade, the president and his wife, Rosalynn, hosted a reception for the three delegations in one of the Camp David lodges.

The first of yesterday's meetings among Carter, Sadat and Begin began at 10:30 a.m. and lasted until 1:35 p.m. It was held in Carter's study in Aspen Lodge, the president's quarters at Camp David.

There has been considerable speculation that most of the American pressure for a settlement would be directed at Begin's refusal to consider Israeli withdrawal from the occupied Arab territory along the West Bank. But Powell, seeking to nip any outbreak of speculation, said nothing should be read into the two American Israeli meetings and suggested there are likely to be separate American Egyptian meetings in the days ahead.

The press secretary also continued to refuse to offer any characterization of what is going on inside Camp David.