Egyptian President Anwar Sadat arrives in Washington today for what the Carter administration regards as a "basic stock-taking" on impediments to Egyptian-Israeli peace talks.

To Sadat the obstacle is simple Israeli obstinacy. Sadat has said he wants to tell President Carter and the American people that they must put pressure on Israel to prevent it from thwarting his dramatic peace initiative.

On the eve of sadat's arrival for an unusually long, six-day visit, Carter administration officials sought to avoid any comments that could be construed as taking sides. Nevertheless, White House press secretary Jody Powell acknowledged there is a continuing American disagreement with Israeli leaders about what they told President Carter concerning new Israeli settlements in occupied Arab territory.

Israeli Foreign Minister Moshe Dayan denied in Tel Aviv on Wednesday that he had promised Carter in September that Israel would refrain from establishing new settlements on the West Bank of the Jordon River. Dayan said the commitment extended only to the the remaining "few months" of 1977.

Powell said yesterday that a recheck of the Carter-Dayan conversation "confirm what the president said at the press conference" on Monday. Carter said that it was "my understanding that no new settlements would be authorized," and that any increase of settlers would be "an expansion of existing settlements . . ."

Although this is a question "of continuing interest," Powell said, he did not want to pursue it in a press briefing.

The settlemnt issue, especially the Sinai desert, which Israel has offered to restore to Egyptian sovereignty, is a special irritation to sadat in the interrupted Egyptian-Israeli diplomacy.

Although this will be one of many issues expected to come up in the Carter-Sadat talks here, the core of the discussions will be on the totality of the American and Egyptian approaches to the peace talks.

Administration officials acknowledge that there is a basic difference in concept between Washington and Cairo, as well as between Cairo and Jerusalem, about how to fulfil the peace initiative which Sadat launched in November. That became glaringly evident when Sadat on Jan. 18 abruptly recalled jis delegation from Political talks in Jerusalem, to the surprise of Secretary of State Cyrus R. Vance, who believed the talks were making progress. All talks are now in suspense, awaiting the outcome of Sadat's Washington visit.

"We need to get on the same wave length" with Sadat, one American official said yesterday.

Sadat was able to produce sensational, initial progress by his public "shock treatment," this source said, but it is now necessary to sort out specific obstacles between Egypt and Israel, and to plan how they can be overcome. This will require time, it is stressed, and the need to convince a frustrated Sadat that the procedd will not bog down into interminable diplomatic nitpicking.

U.S. officials would like Egypt to agree to a more systematic bargaining process with Israel.

At the same time, President Carter must grapple with Sadat's coutcry against the American "arsenal of unlimited arms" for Israel, which Sadat charges is nourishing Israeli intransigence in the negotiations. Egypt now is asking for American F5 Fighter aircraft, and simultaneously, President Carter is weighing decisions on more advanced aircraft for Israel, and for Saudi Arabia, Egypt's ally.

With this array of sensitive issues, the Carter-Sadat talks will take place this weekend in the seclusion of the presidential retreat at Camp David, in Maryland's Catoctin Mountains.

The two presidents, their wives, and variuos senior aides at times, will be at the estate starting this afternoon and continuing until Sunday afternoon. No press briefings are planned there, and officials foreclose "dramatic developments."