President Anwar Sadat of Egypt has told the Israeli prime minister that "it is virtually impossible" to resume Palestinian autonomy talks unless Israel takes "remedial action" to clear the atomosphere created by its policies on Jerusalem and West Bank settlements.

Sadat's warning was contained in a letter to Prime Minister Menachem Begin on Aug. 2 and released today by the Egyptian government, one day after Begin's office released the Israeli leader's firm response to Sadat.

Viewed together, the exchange of correspondence promises a substantial delay in the negotiations unless President Carter can persuade Sadat to back off on his demands or move Begin to revise fundamental Israeli policies he has already said will never change.

Although the content of Sadat's demands had become known over the last 10 days, the text of his letter provided the first glimpse of his personal perception of the current stalemate. In it, the Egyptian leader seems at times almost to plead with Begin not to persist in actions that, in Sadat's view, are preventing the promise of the Egyptian-Israeli peace treaty from fulfillment.

"Dear Prime Minister Begin," Sadat wrote in the letter's closing paragraph, "I am certain that you know, deep in your heart, that it is virtually impossible to continue the negotiations if the present attitude continues.

"Hence in the spirit of my journey to Jerusalem and the Camp David peace accords, I urge you to take the remedial action which is necessary for the removal of the obstacles which have been placed on the road to peace in the past few months."

Sadat added that it is up to Begin to decide which "remedial action" would be sufficient to revive the negotiations, suspended by Sadat for the second time late last month after the Israeli parliament, passed a law declaring all Jerusalem its permanent capital.

At the same time, the Egyptian leader clearly specified that, in his view, three main obstacles lie in the way:

The Jerusalem law, which Sadat called an attempt to "prejudice the outcome of the negotiations."

New Israeli settlements on the West Bank, which Sadat also described as an attempt by the Begin government to create a "nonnegotiable" situation on the ground no longer liable to change through the autonomy talks.

"It was clearly understood, as we signed the (Camp David) accords, that none of us will resort to the imposition of a fait accompli on the other," Sadat complained.

Israel's increasingly tough security measures in the West Bank and Gaza, which Sadat said violate an understanding reached during the October 1978 Blair House talks in Washington to "improve the atmosphere in the West Bank and Gaza as a prelude to the election of the self-governing authority."

"It is obvious that the conditions in the West Bank and the Gaza Strip have not improved ever since," he said. "To the contrary, they witnessed a marked deterioration. Is this the way to win the support and confidence of those who are addressed by the Camp David framework?"

This was a clear allusion to the territory's Palestinian population, which has boycotted the Camp David efforts to set up an autonomous administration. U.S. and Egyptian officials had at the outset hoped to entice West Bank Palestianians into the talks, and even the Palestine Liberation Organization (PLO) leadership in Beirut once had fears this might happen, despite its orders to the contrary.

In the 16 months since the talks began, however, the West Bank leadership has hardened its opposition to the Camp David effort and PLO leaders are now convinced they have nothing to fear from autonomy talks that they now regard as doomed to certain failure.

Sadat, without mentioning specificially the boycott, implied that Begin's policies on Jerusalem and the West Bank have so soured the atmosphere that progress is impossible within the talks as well as in the effort to draw Palestinians into the peace process.

"All along, we were hopoing that the factors which prompted you to take this negative attitude would subside and give way to a more positive and responsive approach," he wrote. "To my regret, these hopes have not materialized and the situation continued to deteriorate. I am referring here to the actions which are being taken with regard to Jerusalem and the settlements, together with the repressive measures taken in the West Bank and Gaza."