With President Carter's acquiesence, the Democratic Party has plunged into the mounting diplomatic furor about the status of Jerusalem and endorsed a platform plank that, if carried out, could trigger a new Arab oil embargo and force Carter to abandon a key element of his own Camp David peace process.

The Democrats' decision to endorse Jerusalem as the capital of Israel came almost at the same moment Wednesday as Saudi Arabia, this country's major source of imported oil, was saying that Israel's handling of the Jerusalem issue had driven all Arabs to give up on any peaceful resolution of the Arab-Israeli conflict.

Observers who have watched the close attention being paid by the Saudi press to both Democratic and Republican conventions and particularly to the Democratic plank on the Middle East suggested that this timing may not have been accidental.

The Saudi statement, delivered by Crown Prince Fahd, the kingdom's day-to-day ruler, appears to be part of a Saudi campaign to resist firmly any erosion of the American position on East Jerusalem, which the Saudis view as a holy Islamic city for which the Saudi royal family bears special responsibility.

Last week, Saudi Arabia and Iraq, currently the two largest producers in the Organization of Petroleum Exporting Countries, jointly announced they would break off diplomatic and economic relations with any country recognizing a new Israeli law which reaffirms all of Jerusalem as the Israel capital.

Fahd, who in May told The Washington Post that Saudi Arabia still hoped for a peaceful solution and would participate in one that guaranteed Palestinian rights, said Wednesday that Israel's new emphasis on its formal annexation of Jerusalem had made a peaceful settlement impossible now.

The Democratic plank on the Middle East was reprinted in full in Saudi newspapers in recent days. It repeats views on Jerusalem contained in the 1976 platform, but it arrives in a radically different regional context, since the Israeli parliament's action on Jerusalem has led Egyptian President Anwar Sadat to suspend the Palestinian automony talks called for by the Camp David treaty.

Moreover, the convention rules requiring Carter to publicly take exception to parts of the platform with which he disagreed have now left the president on the record on an issue that his administration has sought to play down since Sadat and Israeli Prime Minister Menachem Begin signed the peace treaty last year.

The Democratic platform approved Wednesday night states that the party recognizes and supports "the established status of Jerusalem as the capital of Israel" and further urges that "as a symbol of this stand, the U.S. Embassy should be moved from Tel Aviv to Jerusalem."

In his statement, Fahd sharply questioned the whole underlying approach of the Camp David accords toward reaching an agreement with Israel, asking what benefits moderation had brought to the Arab world.

"Is this the West's concept of just peace? And where is the comprehensive peace framework they envisaged, formulated at Camp David and promised us?" Prince Fahd said.

"Hasn't the call for Arabs and Moslems to a long and persistent jihad [holy war] become the only answer to the Zionist religious and racist arrogance?" he continued. "Will the world blame us if, after today, we take matters into our own hands and embark on the defense of Jerusalem and its holy sites against the religious, military Zionist aggression?"

Middle East analysts familiar with past Saudi views and statements on this issue interpreted Fahd's declaration as a deliberate and open attack on the Camp David peace process at a time when President Carter wants to portray it as one of his main foreign policy achievements.

Without naming him, Fahd asked Sadat to stop wasting time on his negotiations with Israel and "to have the dignity to admit failure and courageously to undo what has been done."

The Democratic platform statement on Jerusalem was far stronger that the Republicans, who simply stated that the Holy City "should remain an undivided city with continued free and unimpeded assess to all holy places by people of all faiths."

The Democratic position quotes directly from the 1976 platform regarding Jerusalem. But now, this stand is at variance with the Carter administration's policy in the wake of the Camp David peace accords.

No agreement was reached at Camp David over the issue. But Carter, Sadat and Begin set forth their official views on Jerusalem in letters annexed to the agreement.

In his letter, President Carter reaffirmed that the position of the United States remained as stated in 1967 and 1969 at the United Nations by the then American ambassadors, Arthur J. Goldberg and Charles W. Yost.

The gist of the two statements was that the U.S. government refused to recognize any unilateral action by any of the states in the region to determine the fate of Jerusalem. The Yost statement referred to Israel as the "occupier" and said it had "no right to make changes in laws or in administration other than those which are temporarily necessitated by its security interest."

Only yesterday, the State Department reaffirmed that the United States "doesn't accept nor has it ever accepted, unilateral national legislation dealing with Jerusalem" and said the ultimate legal status of Jerusalem would have to be determined through negotiations among all concerned parties.

The latest Democratic platform position thus stands in total contradiction with both the word and spirit of every official U.S. government statement issued on the subject of Jerusalem since at least 1967. CAPTION:

Picture, PRINCE FAHD . . . calls for new holy war