Israel intends to make good its threat to disqualify from participation in the Sinai multinational peacekeeping force any country that actively supports a Middle East peace initiative outside the framework of the Camp David accords, Israeli officials said today.

The threat, first made almost offhandedly by Foreign Minister Yitzhak Shamir during a speech in the parliament yesterday, was not "casual," but evolved from serious debate within the Foreign Ministry, an official said.

If put into practice, Shamir's Sinai doctrine would exclude virtually every European nation from participating in the multinational force because of the European Common Market's Middle East peace initiative, and could make it difficult for the United States to form a Sinai peacekeeping mission before the April 25 deadline for full Israeli withdrawal from the Sinai.

Prime Minister Menachem Begin also warned European nations not to try to tamper with the Camp David accords or promote an alternative, pointing out that Israel's parliament overwhelmingly rejected a European peace initiative earlier this week.

"There is unity and purpose among Israeli people on this issue," Begin said in a speech in the Red Sea port of Eilat.

Shamir said that Israel has notified all potential contributing countries that "any statement indicating a contradiction" of the Camp David agreement "will disqualify the party so declaring from participating in this force." He added, "Participating in the multinational force must be based solely on the agreement we signed -- we, Egypt and the United States -- in the framework of the Camp David accords. We will not accept anything that contradicts, or deviates from, these documents."

Shamir's effort would appear to disqualify Britain, whose foreign secretary, Lord Carrington, has said that participation in the Sinai force would mean "no weakening" of British determination to press ahead with the European Middle East peace initiative.

Before leaving Riyadh today after three days of talks with Saudi leaders, Carrington repeated his statement, saying that if the Common Market countries take part in the Sinai force, it would be on the basis of wanting to see occupied Arab territory returned to Arabs, and on no other basis.

Saudi Foreign Minister Saud also warned Common Market countries against participation in the Sinai force, saying that could link them too closely to the Camp David process.

Western Europe's reentry into the Middle East process, after a hiatus of months, was prompted by the assassination of Egyptian president Anwar Sadat and fears that the assassination could jeopardize the final stage of Israeli's Sinai withdrawal.

Foreign Ministry spokesman Avi Pazner said that a final decision on Britain would not be made until the British government gives formal notification to the United States that it intends to join the Sinai force. So far, only Colombia, Uruguay, Fiji and the United States have officially joined the force, although Italy, France and Canada have declared the intention to do so.

An Israeli official said that if Carrington, who is chairman of the European Community's Council of Ministers, persists in his statements about the Saudi and European peace initiatives, "this makes things very difficult."

"Israel does not accept any alternative to Camp David. Camp David is the only process which is functional. To bring up any initiative, like Prince Fahd's plan or the European Community's Venice declaration is considered an attempt to create an alternative which will bring about a parting from the Camp David process," an Israeli government official said. The Venice declaration's principles include Israeli withdrawal from occupied areas and Palestinian self-determination.

Defense Minister Ariel Sharon, speaking today at a ceremony to convert a paramilitary settlement south of Hebron to a civilian outpost, said Israel's answer to Saudi Arabia's eight-point peace plan is eight Israeli settlements in the occupied West Bank.

"Israel could have today chosen, in light of the changes, other ways. But Israel has chosen the way of peace, and it will continue to pursue it even if one of the partners, the United States, is starting to eye other plans even if they contain elements which endanger Israel," Sharon said. "We are a nation which believes in building and creation. Our answer to the eight points of the Saudi plan is eight Israeli settlements."