The best evidence that President Anwar Sadat is now in tandem with President Carter following their Camp David rendezvous is the fact that the Egyptian's hard-hitting speech to the National Press Club had undisclosed U.S. blessing.

That speech kept the doors open to resuming political negotiations with Israel and struck hard at Israel on its most vulnerable political point: expanding and building new Jewish settlements in occupied Arab territory. "The Israeli policy of settlements is a shortcut to chaos and lawlessness," Sadat said.

What Sadat did not say was that he had asked Secretary of State Cyrus Vance to read his speech in advance. Nor did he reveal that Vance had no objection to any part of his appeal for help to his receptive American audience.

This teamwork between Sadat and Vance epitomized Carter's strategy: to change Israeli Prime Minister Menachem Begin's hard-line policy for sttlements in the Sinai and West Bank without threatening Israel with reduced American supprot.

"If we put too much pressure on Begin," one official said, "it is absolutely predictable that he will go into trenches. Carter's line has to be low-key but it has to gather irresistible force."

That was the overwhelming consesus of the president and his foreign-policy aides during the long, snowy weekend at Camp David. Most significant, however, was the prominent lead in this direction taken by the two most political players on the presidential team, Vice President Walter Mondale and presidential aide Hamilton jordan.

Mondal is an honors graduate of the political school for championing Israel's cause, right or wrong, on every Arab-Israel issue. So, the vice president surprised others at Camp David with the vehemence of his pro-Sadat arguments on the settlements issue.

The part played by Jordan was no less important. As pointman for selling the president's foreign policy, he has been given a free hand on the settlements issue.

Sadat was made aware that Carter does not intend to let the explosive settlements issue simmer on the back burner. Partly because of Jordan's careful planning. Sadat was privately encouraged by some pro-Israeli figures on Capitol Hill to continue his tough campaign against Begin's policy.

An example is one key Senate aide who has been at the center of pro-Israeli legislative strategy. He fears that unless the settlements issue is resolved in Sadat's favor, a national mood may develop here against Israel with dangerous implications for the future.

This support for Sadat comes on one of the few issues where the United States and Egypt are in total agreement. Blocked from U.S. support at least temporarily on the far more difficult problems of a Palestinian state and final borders, Sadat could not be allowed to leave Washington without substantial satisfaction on future U.S. actions on the settlements. That is about what he had bargained for and exactly what he has gotten, with little fanfare and no White House sermons.

As a result, Sadat goes back to Cairo secure for now that the Carter administration's high command is committed to deflect Begin's self-destructive settlements policy. Following Vance's personal approval of Sadat's harsh language in the Press Club speech, there is a commitment from Mondale, Jordan and lesser White House operatives to push Israel's friends here to influence Begin back in Jerusalem.

Beyond that, Sadat received not very much. But he left Washington in a mood far differnt from the anger that led him to pull his negotiators out of Jerusalem last month.

He will give Vance a couple of months to come up with an acceptable declaration of "principles" on future negotiations agreeable to both him and Begin. Most officials here belive those principles can be drafted.

As always in the Middle East, time is running out. Sadat's trip here was born of desperation, and he got enough support to make it pay this time. But there may not be a next time.