Saudi Arabia has hardened its warning that the United States and other industrial nations are risking a sharp cutback in Arab oil shipments unless they bring more pressure upon Israel to give up its claim to East Jerusalem, according to press reports from Riyadh.

The warnings are being taken seriously by experts in the United States, although they hold differing opinions on how deeply Saudi Arabia might cut production if it takes that course laterthis year.

Some experts believe that the Saudisare considering a moderate cut from the current production level of 9.5 million barrels a day, down to the official production ceiling of 8.5 million barrels a day or a little under that. Supplies of crude oil and petroleum products are so large now that a cutback of that order should not cause shortagesor a price spurt, provided the action didn't set off a wave of panic buying, experts say.

Other authorities see in the Saudi warning a repeat of events early in 1973, when a succession of public warnings from Saudi Arabia and other Arab nations were followed by the Arab oil boycott.

"I just don't know how to take it," said John Lichtblau, head of Petroleum Industry Research Associates, a respected international oil analyst. "It can't be ignored."

A report Wednesday from Saudi Arabia in Platts Oilgram News quoted unnamed Saudi government officials as confirming that discussions are under way to coordinate "drastic production cuts with other Arab oil exporting countries" if the western industrializednations fail to bring pressure on Israel to change course on East Jerusalem.

A decision could be expected in November, following the U.S. presidential elections, the report said,noting that the Organizations of Petroleum Exporting Countries will becelebrating its 20th anniversary that month in Baghdad, and Arab League will be meeting in Amman, Jordan, in November.

The action by the Israeli parliamentto annex Arab East Jerusalem and joined it with West Jerusalem as the undivided capital of the Jewish state has produced as rising, increasingly sharp reaction from Saudi Arabia and other Arab States.

The reported statement Wednesday raised the possibility of specific cutbacks in Saudi production. "We could go to 7.5 million barrels a day, and then the next month drop to 6.5 million and so on," said the unnamed "senio Saudi government official" quoted by the Platts report.

The reports were accepted as accurated by officials of several U.S.-based companies, although they said they had no independent confirmation of them. "There are no unofficial spokesmen in Saudi Arabia," said one U.S. oil official. None was willing to be quoted by name because of the sensitivity of the issue.

Saudi Arabia's current oil policies support the optimists' view that a severe embargo is not in the offing, assuming the Arab-Israeli conflict does not continue to escalate.

The Saudis boosted oil production following the revolution in Iran to offset the shutdown of Iranian oil fields early in 1979, and Saudi production continues at a high 9.5 million barrels a day, 1 million barrels above their official production target.

Their purpose was to restore price stability by creating a worldwide surplus large enough to end the frantic scramble for oil stocks that followed the Iranian revolution.

The strategy has largely succeeded, thanks to increased production not only from Saudi Arabia's fields, but also from Iraq, the North Sea, Mexico and Alaska's North Slope. Oil prices have stabilized, and by Oct. 1 the oil stockpiles of the 21 nations supporting the International Energy Agency are expected to reach about 436 million tons, a 91-day supply. The comparable average for the previousthree years was 79 days.

Ecuador yesterday abandoned its official minimum prices of $36 a barrel, recognizing that it must trim prices to sell its oil in a glutted market. Other OPEC producers have been forced to reduce price surcharges for the same reason, and complaints about Saudis' contribution to the worldwide stockpiles have been increasing from other Arab oil producers.

Some observers believe the Saudi warnings foreshadow a moderate reduction that would tighten world supplies and end the current price cutting, but would not lead to shortages. Having regained a controlling position on world oil prices, the Saudis can be expected to heal political differences with other Arab states, some analysts say.

"A one-million-barrel cutback would be doing the oil companies a favor," said one industry official.

Others note that the Saudis have a history of following through on their public pronouncements. "When they start talking, they usually mean it," one oil company official said.

Earlier this month, Saudi Crown Prince Fahd called for a "holy war" against Isreal to end its occupation ofEast Jerusalem and the West Bank, and the statement about oil production cutbacks should be read in conjuction with that warning, an oil company official said.

The official noted that the report from Riyadh said Saudi Arabia would not act alone. A sharp cutback by Arab oil producers generally would be too great a shock even for the huge world oil stocks, this official said.