Energy Secretary James R. Schlesinger said yesterday the Carter administration may ban Sunday gasoline sales and force other mandatory conservation measures if Iran does not begin exporting oil by April 1.

While comparing the Iranian oil shutdown with the 1973 Arab oil embargo, Schlesinger cautioned that mandatory cutbacks in oil supplies would not be necessary if the public responds to conservation appeals.

So far, Schlesinger told reporters yesterday, "The position of the U.S. has not been dramatically affected" by Iran's virtual cutoff of oil exports.

Schlesinger said the drop in Iranian oil sales "is just beginning to bind now," and that some domestic refiners will begin to face shortages of crude oil. The administration will determine by April 1 whether to impose mandatory conservation measures.

Energy Department planners are weighing various conservation measures that could be submitted to Congress for approval, including: banning Sunday gasoline sales, which might save 150,000 to 300,000 barrels of oil a day; imposing restrictions on commuter parking, which could save 100,000 to 175,000 barrels of oil a day, and imposing emergency heating and coloing restrictions on temperatures, which could save 200,000 to 350,000 barrels of oil a day. These actions, department officials stress, are still in the planning stage, with the estimated oil savings representing "an illustrative range."

Together, they would save less than 10 percent of total U.S. daily oil imports.

Schlesinger described rationing as much more of "an ideological issue" and said it probably would not be needed to manage an oil shortage.

Much of the oil production from Iran, once the world's second leading oil exporter, has been made up by other oil producers, most notably Saudi Arabia. Iran was producing up to 6.5 million barrels a day before the political upheaval that forced the shah from power. Schlesinger has continued to say that, as a result, world supplies are short about 2 million barrels a day.

The United States is less dependent on Iranian oil than most other industrial countries, such as Japan.

Schlesinger and State Department officials said yesterday that members of the 19-nation International Energy Agency, based in Paris, have yet to call for triggering of a plan to force the United States to share its oil supplies with the other industrial countries.

Under an IEA agreement negotiated after the Arab oil embargo, member countries can trigger the sharing agreement when their supplies are 7 percent less than normal consumption.

Under the 1975 Sinai accords, the United States guaranteed Israel's oil supply in the event of an emergency. Until the cutback, Iran provided Israel with 70 percent of its oil.

Schlesinger said that there have been discussions with senior Israeli officials in recent weeks over how the United States would fulfill that agreement. Israel has not asked for U.S. supplies, but Schlesinger said the Israelis should expect 60 to 90 days' lead time. "One of the best systems would be to allow exports from the North Slope" of Alaska, the secretary said. This would require congressional approval.

Middle East Economic Survey, an authoritative trade journal, reported this week that Saudi Arabia would limit its production during the first quarter of this year to 9.5 million barrels a day -- down from nearly 10.5 million barrels now.

This report, which has been confirmed by informed sources, originated at a Jan. 15 meeting that Saudi Oil Minister Zaki Yamani had with the members of the Arabian American Oil Co. -- Texaco, Exxon, Mobil and Standard Oil of California. The same information, sources say, has been transmitted from the U.S. embassy in Jiddah to Washington.

Asked about whether the critical Saudi production level had been unequivocally limited to 9.5 million barrels a day for the first quarter, Schlesinger said yesterday, "I think not. There is some question whether that will be the case."

The Aramco companies have all declined to comment publicly.

In some industry circles, there has been speculation that the Saudis' announcement could be tied to dissatisfaction over U.S. handling of the Middle East peace talks, as well as an effort to respond to conservation pressures within the kingdom.This is denied by administration officials.

"It is a most delicate issue," said one senior administration official, corroborating Schlesinger's comments, and at the same time confirming that the U.S. embassy had reported the 9.5-million-barrel ceiling to the State Department.

The official said that the United States is awaiting further confirmation from the Saudis, adding that it is still possible they would go above 9.5 million barrels of oil during the first quarter.

Administration officials privately express concern over the impact a cut in Saudi production could have on exchange rates and oil prices, and say they expect the Saudis to clarify their position soon.

On other questions, Schlesinger said:

DOE is prepared to allocate oil supplies, and is circulating regulations to allow oil industry companies to update their positions under DOE regulations to reflect changes in the market since 1973.

Gasoline prices are likely to go up 12.2 cents in the next two years.

The Central Intelligence Agency knew Mexico had 140 billion barrels of estimated recoverable oil before the Carter administration unveiled its energy plan in 1977, but he thought that Mexico would probably adopt a moderate oil development plan.

There is uncertainty about the size of China's oil reserves, but it is likely they could have 50 billion barrels onshore and 50 billion barrels offshore.