The Carter administration will decide in a "couple of weeks" if it can gain enough support for the Panama Canal treaties to push for a Senate vote this fall, co-negotiator Sol M. Linowitz said yesterday.

President Carter yesterday completed his unusual week of talks with Western Hemisphere heads of state who assembled for ceremonies to sign the treaties. Now a national "educational process" will be launched in the administration's drive for ratification, Linowitz said at the State Department.

Although Senate Majority Leader Robert C. Byrd (D-W.Va.) publicly has forecast a vote in the January-February period, Linowitz said the administration will seek a vote before the year-end recess of Congress "If the (supporting) votes are there."

White House and State Department head counts indicate "there may be in excess of 50 votes already" for the 67 Senate votes needed, Linowitz said, but other counts differ.

Sen. Paul D. Laxalt (R-Nev.), announcing a conservative's campaign to send "truth squads" around the country to oppose the pacts, said the administration has "completely misgauged sentiment on this issue."

He estimated that there are now 25 senators ready to oppose the treaties, nine short of the one-third-plus-one needed to block them. If a vote is put off until next year, Laxalt said, "our chances will improve with time."

The foreign policy issues that will increasingly compete for attention were in evidence yesterday as President Carter reiterated that Israel's establishment of settlements in occupied territory create "additional problems" for an Arab-Israeli peace settlement.

Carter's comments were made to reporters as he said farewell to Argentina's President Jorge Rafael Videla.

Reporters were questioning Carter about interviews by Israeli Agriculture Minister Ariel Sharon, projecting extensive expansion of Israeli settlements in the occupied West Bank of the Jordan River. Sharon was a bold general in the 1967 and 1973 was with the Arabs.

Carter said the Israeli settlements will be included in the agenda when he meets with Israeli Foreign Minister Moshe Dayan. Those talks are due to begin Sept. 19. When a reporter said Israel's action appears to be "defiance" of U.S. policy, Carter replied, "You have analyzed it very well."

Spokesman Hodding Carter III said yesterday that State Department has been again assured by Israel "that no settlements have been established in the occupied territories beyond those announced."

Sharon was reported to have said in a newspaper interview that several Jewish settlements have been secretly established during the past month. In a subsequent British television interview he said his remarks had been misinterpreted.

Sharon, in a new interview in the Jerusalem Post, said that, although it "sounds like a dream," in 20 to 30 years there would be a corridor of Jewish settlements with 2 million inhabitants in the West Bank, parallel to Israel's present heavily populated coastal strip. Many Israeli officials scoff at Sharon's projections.

Asked how this will be done over American opposition, Sharon said, "it will change." He said, "Look, I welcomed the election of Jimmy Carter as President, and I still do; I greatly resented pressures to which we were subjected by the Ford administration. But at it [the Carter administration] is a passing phase compared with our long-range goals."