The chairman of the National Iranian Oil Co. appealed to the country's Moslem opposition leaders today to help resolve the spreading strikes that have paralyzed the economy and are increasingly threatening the rule of Shah Mohammad Reza Pahlavi.

The strikes are disrupting the operation of the shah's military-led government and eroding its authority even more than the continuing street demostrations in defiance of martial law in Tehran and provincial cities, diplomatic sources said.

The past week's turmoil has almost eliminated the prospect of a new civilian government under a "constitutional" shah with reduced powers, a solution favored by U.S. officials but which other analysts here never really considered viable.

In response to the increasingly anti-American tone of recent street violence, the U.S. Embassy warned Americans to "serverely limit their travel in Tehran over the next few days." The advisory, which underlined earlier warnings to Americans to avoid trouble spots, said: "We suggest that you stay home as much as possible when you do not have to go to work."

The leader of the religious opposition, Ayatollah Ruholla Khomeini, said from exile near Paris that next Saturday will be another day of national mourning marking the first anniversary, by the Moslem calendar, of the day on which troops gunned down protestors in the holy city of Gom, setting off the year of turmoil that has grown from a nuisance into a genuine threat to the shah's survival.

On the surface, at least, Tehran seemed calmer today than any time this week. Fewer mob incidents were reported and the streets often seemed deserted as traffic thinned because of the gasoline shortage.

Witnesses reported several shootings by martial law forces against street protests, however, and an Iranian cameraman said that on one street in east Tehran he filmed the bodies of 15 demonstrators shot by soldiers.

Opposition sources reported demonstrations and shootings in provincial cities across the county, notably in the oil center of Ahwaz in southwestern Iran where, they said, 30 persons were killed in the streets. In Tehran, cars lined up in front of gasoline stations, bakeries and kerosene shops. The government announced that municipal garbage collection is stopping because there is not enough fuel for the trucks. Bus service already has been suspended for the same reason.

In statements broadcast by official Iranian radio, oil company chairman Abdullah Entezam said the government is considering further petroleum imports from "neighboring countires" to help meet demand. But he expessed hope that these purchases would not prove necessary and called on leaders of the Shiite Moslem opposition to use their influence to persuade oil workers to return to work.

Entezam said today's production dropped to 200,000 to 300,000 barrels, compared to the full capacity of 6.5 million barrels a day during a period of high international demand as oil companies build up stocks before the price increases decreed by the Organization of Petroleum Exporting Countries to take effect Jan. 1.

However, production levels are academic, industry sources say, because the county's refineries are largely closed.

"There is a complete shutdown," an oil company spokesman said. He said the country's oil fields and refineries are effectively inoperative and that Iran, normally the world's fourth-largest producer and second biggest exporter, is no longer exporting oil at all.

In addition to the radio appeal, the company is making informal contacts with leaders of the Shiite opposition based in Qom, 90 miles south of Tehran, to urge a return to work industry sources said.

A top company official also has been dispatched to Khuzestan Province, the main oil-producing region, to persuade strikers to at least produce enough to meet domestic consumption.

Entezam said fuel is not being rationed, but that the state-run distribution system has been ordered to give priority to hospitals and place with the coldest climates. He said there was no plan to issue ration coupons for gasoline or kerosene.

Authorities had said yesterday Iranians would be limited to the equivalent of 6.6 gallons of gasoline and 5.2 gallons of kerosene per purchase because of the shortages. Some service stations in Tehran were abiding by the limit today, others not.

A Western oil official said that in any case it would be "ludicrous to talk about rationing" when there is virtually no production or refining.

"It's too late for rationing," he said. "The rationing now is deprivation."

The opposition National Front blamed the fuel crisis on the government, claiming production could meet domestic needs, but that military authorities were holding back distribution to squeeze the population in hopes of provoking a backlash.

Diplomats and oil industry sources said the oil field strikes are in large measure the result of fear following the assassination of two oil officials -- an American and an Iranian -- and intimidation by hard-line strike leaders. But some diplomats said the government is doing little to ease the situation, perhaps in hopes of reversing opinion.

"I think the government has decided to let the people stew in their own juice and hope it will turn them against Khomeini," one diplomat said. The exiled religious leader has ordered oil workers to continue the strike "until the shah's departure."

Well connected Iranian sources now rule out a political solution to the present crisis through the installation of a civil government under a former National Front official, Gholam Hussein Sadighi. Given the events of the past week, the sources said, Sadighi's efforts to form a new government under the shah have collapsed, since no opposition or neutral figure is willing to join such a Cabinet.

As a result, the sources said, the shah is coming down to a choice between giving up the throne he has occupied for 37 of his 59 years or ordering an all-out military crackdown.

A spokesman for the shah's imperial court continues to deny that the former is even under consideration. And should the shah choose the latter, political analysts say, he would risk the long-feared open rift in the military and would by no means be certain to crush the opposition and end the strike even if the army held together.

A third possibility is that the Iranian armed force -- still considered loyal to the crown -- would ask him to step down for the good of the country. Tehran is awash with the inevitable rumors that such a move is in the offing. But analysts here have no reading on this possibility, nor on that of another product of the rumor mill: a "colonels' putsch" to overthrow the monarch.