Secretary of State Cyrus R. Vance said yesterday the United States considers Israel's settlements in the Sinai desert as "contrary to international law and therefore should not exist."

"Our position on this is quite clear," Vance said in a statement that broke no new ground of U.S. policy in the Middle East but that was notable for its relatively blunt tone. He added, though, that an agreement on dismantling the settlements was a matter for negotiation between Egypt and Israel.

Speaking at a press conference, he equated the Sinai settlements with the status of the Israeli-occupied West Bank and Gaza Strip "and the intertwined Palean question" as the principal obstacles to peace in the Middle East.

Vance's comments, which followed the visit here this week of Egyptian President Anwar Sadat, appeared to lend backing to Sadat's contention that Israel must make further concessions on these issues if there is to be any progress in the stalled Egyptian-Israeli peack talks. Vance said he would pursue these points when he meets with Israeli Foreign Minister Moshe Dayan next Thursday.

"These two problems must be overcome if we are going to make progress in these negotiations," Vance said. "The continued settlements activity by Israel creates an obstacle to peace and must be faced up to and dealt with in order to make progress."

Israel, he said, should halt further construction work on its Sinai settlements. He also questioned whether "archeological" work being done at the new Israeli West Bank Settlement at Shiloh was genuine.

Vance also repeated past U.S. calls for turning the West Bank and Gaza Strip into a Palestinian homeland linked to Jordan, with an interim period during which these areas would be under some kind of international control to allow time for working out details of a agreement.

Vance said President Carter has not yet decided about an Egyptian request to purchase U.S. arms. The White House said, meanwhile, that Carter would study the request, which includes jet fighters, while he spends the weekend at Camp David, the presidential retreat in Maryland.

In commenting on the Egyptian arms request, Vance differed with Begin, who said Thursday that such a sale would threaten peace in the Middle East. If the Carter administration's criteria for arms sales are applied carefully, Vance argued, "it would be possible to make arms sales which are not disruptive" of the military balance in the region.