The Israeli Foreign Ministry sharpened its attack on Egyptian President Anwar Sadat's new peace proposal yesterday, saying that upon closer examination the plan contains no elements that Israel could seriously consider.

Foreign Ministry officials expressed growing pessimism over the prospects for next week's foreign ministers peace conference in London, and suggested that the conference could lead the United States into submitting peace proposals of its own.

As recently as last week Israeli Foreign Ministry officials, while condemning the plan as largely unacceptable in its present form, said it contained some "positive" provisions that could at least pave the way to serious negotiations on some issues.

These included Sadat's omission of any reference to the Palestine Liberation Organization or to the creation of a Palestinian state, and the inclusion of a proposal for dismantling Israel's military government in the West Bank and Gaza Strip that closely parallels a proposal in Israel's own Middle East peace plan.

Yesterday, however, two high-level Foreign Ministry officials, including Israel's chief international legal adviser, dismissed those provisions as "negative" and said Sadat's plan was designed more to be rejected than accepted.

Meir Rosenne, the Foreign Ministry legal adviser, called Sadat's plan a "change to the worse" from positions reached between Israelis and Egyptians in talks in Jerusalem and Ismailia.

While conceding there is no reference to the PLO, Rosenne said, "But if you read the text, there is nothing that would be contrary to the PLO. Nothing that would prevent the PLO from becoming a party to these negotiations."

Rosenne said that while the term Palestinian state is not used, "In fact, you have a reference to Arab authority." He was referring to a provision that calls for U.N. supervision of Israeli withdrawal from occupied territories and the "restoration of Arab authority."

Rosenne was also sharply critical of Sadat's proposal that the military government be absolved, which he called "a demand regarding the end of Israeli presence" in the West Bank and Gaza.

Zalman Shoval, a key adviser to Foreign Minister Moshe Dayan, who said he was speaking as a member of parliament, called the Sadat proposal "extremist" and said it is "a retreat not only from Jerusalem and Ismailia, but a retreat from Sadat's own statements."

Under the plan, Shoval said, "eventual inclusion of the PLO is almost a foregone conclusion. There is a very good possibility the PLO would share part of this land once Israel withdrew."

Shoval, in an interview, was critical of the suggested inclusion of the United Nations in negotiations, saying, "We are not enthusiastic about the participation of the U.N. in any process, not only because of the events in Lebanon . . . But because of the sum total of its (member) components. Who can assume the U.N. would be objective?"

Asked whether Israel's increased attacks on the Sadat plan were designed to forestall blame if the London talks fail, Shoval said, "There is something in what you say. Sadat has been stage directing this in a masterful way. Certainly Israel does not want to get blamed."

Shoval said that "the view of the Foreign Ministry" is that Israel has been manuvered into a position where it inevitably will reject Egypt's proposals formally at the London conference, which will just as inevitably lead to the submission of new ideas by the United States.

Yesterday's notes of pessimism underscored what is reported to be the mood of Dayan, who was quoted in The Washington Star Monday as having told Vice President Mondale that the London talks with "turn out to be a waste of time" but that he would go to London anyway to "see some shows I missed."

The Foreign Ministry yesterday denied the Star quotations, purportedly from a transcript of the Dayan-Mondale meeting here, saying, "These sentences are not quotations from the protocol of the talk and do not reflect the contents of the talk."

The ministry specifically denied several of the more pointed quotations, as did a U.S. official who sat in on the meeting.The U.S. official said that while several people took longhand notes, there was no verbatim transcript.

An Israeli official knowledgable about the talks, however, said that the Star's account reflected in general terms the foreign minister's attitude.

The official, who asked that he not be named, said, "Dayan thinks all they [the Egyptians] will want to talk about is the Sadat plan, and that there will be no real rapprochement." He added that Dayan does not think that Egyptian Foreign Minister Mohammed Ibrahim Kamel "has the flexibility to do anything without going straight to Cairo."

The Foreign Ministry also denied a report in the Jerusalem newspaper, Davar, that Dayan told Mondale the United States creates a negative image of Israel, and that he doubted the United States wants to alleviate the tense atmosphere between the two countries.