U.S. national security adviser Zbigniew Brzezinski and roving ambassador Alfred Atherton arrived here today to begin what a high-ranking Egyptian official called "the final sprint to peace" between Israel and Egypt.

They are here to prepare for the visit of President Carter, which starts Thursday and is aimed at overcoming the remaining obstacles to the conclusion of the peace treaty Egypt and Israel committed themselves six months ago to seek.

Shortly after his arrival, Brzezinski met for two hours with President Anwar Sadat. A U.S. spokesman said they conducted a "wide-ranging preview in a general way of what President Sadat and President Carter will be covering during Carter's visit," but he gave no details.

Carter, who is scheduled to leave Washington late Wednesday, hopes for a vast outpouring of Egyptian public support to enhance the treaty's chances, a White House official said in Washington.

"That demonstration of support can have only a positive aspect throughout the Middle East," he said, "and it would also be reassuring to the people of Israel."

Carter also hopes that by going to Egypt he can touch off public support for Sadat as well as for the peace treaty, according to White House officials. U.S. officials recognize that any further concessions by Sadat will endanger his already shaky standing within the Arab world.

To spark these public demonstrations, U.S. and Egyptian officials are planning a gala motorcade from the airport into Cairo and, on the second day of Carter's visit, a train trip from Cairo to Alexandria.

The White House official cautioned that "there's no way we could conclude a peace treaty, with all it would take," during Carter's Middle East trip. He said, however, that he would not rule out the initialing of some sort of agreement.

Although official caution and reticence prevail here, the Egyptians do not seem to be worried about the possibility that the proposals Carter is bringing will be rejected or that a trip now shaping up as a joyous occasion could end in failure.

Some skeptics, recalling that the entire peace process appeared to have ended in dismal failure only two days ago, were warning against overoptimism. "I still don't think there is going to be any agreement," one veteran political observer said tonight.

Some Foreign Ministry officials are also anxious about the possibility that Carter, in his determination to wrap up a treaty, might yet squeeze Sadat into accepting terms that will only inerease Sadat's isolation in the Arab world.

There is also widespread concern among officials, newspapers and politicians that a peace treaty might be concluded but then fall apart later in haggling over its implementation, especially on the Palestinian issue.

But the government is organizing Carter's trip as if success were assured, and popular enthusiasm for the visit has stirred some of the old forgotten excitement about the possibility of imminent peace. Even the contingency plans for a treaty signing on Mount Sinai have been dusted off.

Carter is scheduled to address Egypt's parliament on Saturday. The Egyptians, anxious to show popular support for Carter and perhaps also to show him their need for finanical aid, pressed him to visit Alexandria, traveling through the heartland of agricultural Egypt as Richard Nixon did in 1974.

Very little of substance has been revealed about the actual negotiations. Reporters were barred from the airport when the U.S. delegation arrived, with photographs permitted only from a distance, and the press was also excluded when Brzezinski saw Sadat this evening.

It was not even stated officially that Brzezinski was bringing Sadat the compromise formulas on the remaining issues that Carter submitted Sunday night to Israeli Prime Minister Menachem Begin.

Egyptian Ambassador to Washington Ashraf Ghorbal told reporters, however, that the meeting between Sadat and Brzezinski would constitute "the first detailed discussion of the American proposals here in Egypt."

By late tonight, no further American -Egyptian meetings had been Officially scheduled, but at least one session with Prime Minister Mustapha Khalil is expected before Carter arrives.