President Reagan assured Egyptian President Hosni Mubarak yesterday that the United States will continue "the leading role" in efforts to resolve the Mideast crisis, but U.S. officials conceded that the two governments disagree about how to deal with Israel and the Palestine Liberation Organization.

That became apparent after Egyptian Foreign Minister Kamal Hassan Ali gave Reagan a letter from Mubarak that reportedly calls for linking a Lebanon solution to a comprehensive Arab-Israeli settlement that recognizes the Palestinians' right to self-determination.

Hassan Ali, who later conferred separately with Secretary of State George P. Shultz, told reporters that Egypt would like to see greater U.S. pressure on Israel to lift its siege of West Beirut and allow the Arab world to resolve the problem of PLO withdrawal from the beleaguered city.

"Our point of view has always been that moving PLO forces from Beirut must be an Arab endeavor and not taken under military pressure from Israel and that it should be linked with hope given to the Palestinians and hope for a just and comprehensive settlement to the Palestinian question," he said.

The idea of such linkage, including the start of a U.S. dialogue with the PLO in exchange for its recognition of Israel, has been reiterated persisently by the Mubarak government since Israel launched its invasion of Lebanon on June 6.

The Egyptians have sought to make this linkage a condition of their willingness to provide refuge in their country for some of the PLO members trapped in Beirut. It also is the basis of a draft resolution jointly introduced by Egypt and France in the U.N. Security Council on Thursday.

However, the administration, while officially open-minded about the French-Egyptian initiative, privately is known to believe that such linkage cannot be accomplished at this time.

The U.S. view is that priority attention first should be focused on getting the PLO out of Beirut without further bloodshed. In addition, U.S. officials are concerned that the French-Egyptian initiative might provide PLO leader Yasser Arafat and his supporters in the international community with an opportunity for further stalling that would undercut the efforts of Reagan's special envoy, Philip C. Habib, to negotiate a PLO withdrawal from Lebanon.

However, a senior administration official who briefed reporters at the White House stressed that Mubarak remains America's closest ally in the Arab world, and asserted that the differences between the two governments involve tactics rather than goals.

The official, who cannot be identified under the rules of the briefing, said Reagan and Hassan Ali had agreed that both governments should redouble their efforts toward a Mideast peace "with priority on an early solution of the Palestinian question in all its aspects." But he refused to discuss specifics of how the president responded to Mubarak's call for a dialogue with the PLO or the conditions under which PLO forces might be accepted into Egypt.

Hassan Ali said the meeting with Reagan had convinced him more than ever that the United States will continue "playing the leading role in solving the Middle East problem in a way that would ensure the security and rights of all nations and peoples of the area . . . . "

Sen. Paul E. Tsongas (D-Mass.), returning from a five-day trip to the Middle East, warned that irresolution over the Lebanon crisis could provoke a superpower confrontation and called for the United States to increase its pressure on Israel and the PLO's Arab backers.

"It is time for the Arab countries to make clear to the PLO that the war against Israel is over," Tsongas said. But he added that Israel's policies do "not address adequately the Palestinian issue . . . . "