A new U.S. special envoy today launched his effort to breathe new vigor into the Middle East peace talks amid fears in Egypt that the talks have lost priority within the Carter administration because of the pressures of the presidential campaign and the Iranian crisis.

Sol Linowitz, who assumed his post after Robert Strauss resigned last month to head President Carter's re-election campaign, began two days of talks here today. He immediately attempted to reassure the Egyptian leadership that there is still a sense of urgency in the United States about the Middle East.

"Despite the gravity of the crisis facing the United States," Linowitz said on arrival, "let me assure you that the president of the United States and the American people are more firmly resolved than ever to succeed in the venture in which we are engaged."

Linowitz, who is to go to Jerusalem next week for talks with Prime Minister Menachem Begin's government , is on his first visit to the region since taking the post and is expected to mark a new style after the down-home wheeling that Strauss brought from Texas.

Even before Strauss stepped down to run President Carter's reelection campaign, however, the negotiations deliberately had been steered toward low-level technical subjects. This was decided in an effort to avoid an early standoff on substantial differences, such as the definition of West Bank and Gaza autonomy or the place of Jerusalem's Arab residents among Palestinians allowed to vote for the autonomous administration.

The lack of progress on such key issues had prompted Boutros Ghali, the Egyptian minister of state for foreign affairs, to organize a task force to consider where Egypt could turn next if the talks fail to reach some kind of accord by the May 25 deadline set for their completion. Egypt was considering a call for a new Geneva conference under U.N. auspices and yesterday officially welcomed a resolution by the U.N. General Assembly calling for "prompt convocation" of such a conference.

"Now comes this Iranian thing. . . It is just terrible," said a high official in the Foreign Ministry, underlining the added concerns.

Washington's standoff with Iran is likely to make progress in the talks difficult for several reasons, Egyptian officials say. For one, it has absorbed Carter and his top aides in the White House and State Department who are responsible for Middle East affairs, dissipating any pressure for swift progress in the Palestinian negotiations, they say.

Ghali reminded visitors last week, for example, that Assistant Secretary of State Harold Saunders, regarded here as the key actor in the State Department on the autonomy talks, also is running the department task force on Iran and thus has turned his attention from the Egyptian-Israeli problem.

In addition, Egyptian officials fear the climate created by Iran's Islam based calls for opposition to the United States is likely to sour American public opinion toward the Arab case against Israel. This is particularly true of the Palestine Liberation Organization, they add, which has identified itself with the Iranian revolution just as it seemed to be making progress in Europe and the United States in building an image of moderation and respectability.

Some observers here express belief that President Anwar Sadat had these dangers in mind when he repeatedly offered an Egyptian haven to the ailing shah, citing Islamic principles and hospitality and generosity.

Any U.S. military moves against Iran also would stir up Arab public opinion against the United States and pressure Egypt to show reserve in its friendship, the officials predict. "That would be the worst thing that could happen," said one Foreign Ministry official. "America's Arab friends would have to become very shy friends for a while."

The Iranian crisis, viewed from Cairo, is doubtly damaging to the autonomy talks because it is unfolding at the start of the U.S. presidential campaign, considered across the Arab world as an obstacle to any U.S. policy opposed by Israel. Since Egypt is counting on the United States to pressure Israel into concessions on the West Bank, electoral considerations in Middle East policy are seen as a new complication in an already difficult situation.

As an example, Egyptians cite the recent declaration by Sen. Edward Kennedy (D-Mass.) that Israeli refusal to deal with the PLO has been proved right by the Iranian taking of American diplomats as hostages in Tehran.

The Iranian crisis and U.S. electoral needs are regarded here as particularly unfortunate. Egyptian Foreign Ministry officials expect increased Arab retaliation against Sadat when Egypt and Israel exchange ambassadors, scheduled for Feb. 25. To counter the opposition, they would like to present the Arab world with visible progress in the peace talks before then.

"Unless we have that, the exchange of ambassadors will be the consecration of the charges that we have made a separate peace," one official said.

Ghali has voiced determination to measure the progress of normalization after ambassadors are exchanged by the rate of Israeli concessions in the autonomy talks. In the past, however, Sadat has ordered accommodation with Israeli demands despite reticence in his Foreign Ministry, and diplomats in Cairo expect similar pushes from above over the six-month normalization period scheduled to begin once the ambassadors are in place.

Sadat himself makes the decisions on dealings with Israel, they point out, and so far appears determined to maintain the good relations established with Begin despite lack of progress in the autonomy negotiations. The Foreign Ministry repeatedly has taken a harder line than the President himself, they recall.

Linowitz is scheduled to see Sadat Sunday afternoon, after his preliminary meetings this evening with Ghali and Vice President Hosni Mubarak and a Sunday morning discussion with Prime Minister Mustafa Khalil.

Egyptian officials have been reluctant to comment on the personality of the new envoy, pleading lack of knowledge. Some concern has been expressed, However, about his apparent willingness to work without direct access to Carter. Although Strauss' unorthodox style irritated some Egyptians and his knowledge of the Middle East was considered inadequate, his standing in the White House was respected.