The nearly week-long Middle East summit conference entered a new "more intense" phase yesterday with the participants, for the first time, exchanging written documents that set out where each side stands in the complete negotiations at nearby Camp David.

White House press secretary Jody Powell described the activity at the presidential retreat as an "even more intense and detailed" effort "to see if approaches can be found to deal with those important areas of substantial difference" that remain between Egyptian President Anwar Sadat and Israel: Prime Minister Menachem Begin.

Yesterday morning, President Carter met alone for two hours with Sadat, following up a similar meeting he had with Begin on Sunday.

Part of the activity, it was learned, involved each of the three delegations drafting statements on where the talks stood, followed by meetings to agree on wording in the beginning of a process to produce some kind of concluding statement or agreement for the summit.

However, the officials continued to refuse to supply anything but the sketchiest information about the talks. It was impossible to determine whether the "apparent progress" that Powell has mentioned to reporters would hold up or simply evaporate because of the remaining differences.

The three leaders have been at Camp David since last Tuesday, escaping the comfortable confines of the presidental compound for only a few hours Sunday to tour the Gettysburg Civil War battlefield. The summit is now expected to last at least until tomorrow and possibly later.

Briefing reporters yesterday, Powell described the summit as following a now "well-established pattern" that saw Carter first meet separately with Sadat and Begin, then bring them together for almost seven hours of trilateral talks and now resume separate sessions with them in an effort to persuade each to compromise further.

The three leaders have not met together since Thursday, prompting questions here about a possible deadlock in the talks.

"I don't think it would be appropriate to draw (the) conclusion of stalemate," Powell said when asked about this.

Powell said he expects additional meetings of the three leaders, probably beginning today.

On Saturday, Powell released a statement, agreed to by all three delegations, declaring that "progress does seem to have been made" at the summit but that "substantial differences still remain. "The statement's wording and later comments by U.S. officials emphasizing the differences were prompted in part by American fears that reporting of the summit was growing too optimistic.

It has been the U.S. strategy from the first to set the lowest possible expectations for the summit's outcome and in that context, the Saturday statement appears to have had its intended effect. Just as the meetings have followed a clear pattern, the impressions of observers at the press center here have followed a cycle-from guarded optimism after the first few days of growing pessimism over the weekend.

Powell, meanwhile, sought to position himself squarely between those two feelings. "I think neither optimism nor pessimism is particularly justified at this time," he said yesterday.

Powell also said that Carter "is most likely to report in some fashion to the public and to the Congress about the conference" after it is concluded.