The nominee of Iran's clergy and the nation's largest political group dropped out of the presidential election race today, improving the prospects of the only candidate who has urged a speedy end to the crisis over American hostages here.

Religious support previously given to Jalalledin Farsi, who withdrew today, now is expected to swing to radical economist Abol Hassan Bani-Sadr, who has long proposed a quick decision to release or punish the hostages. Election day is Jan. 25.

As the confrontation with the United States entered its 11th week, Iran's coordinator of the foreign press said that yesterday's decision to expel American correspondents may help resolve it by shifting U.S. attention from the hostages and their militant captors in the U.S. Embassy.

In ordering American journalists to leave the country by midnight Friday, Iranian authorities will help isolate the embassy occupiers, who attract large crowds each day to shout radical slogans at American television cameras. l

The embassy militants, with their popular support, have complicated government efforts to find a solution that falls short of the captor's persistent demand for the return of the deposed shah before any of the Americans are freed.

If the captors "are really looking for publicity," said Abol Ghassen Sadegh, who oversees foreign correspondents for the National Ministry of Guidance, "and I don't believe they are, this [mass expulsion] will ease tensions."

Others believe there will be no significant movement toward a solution at least until after the presidential elections, the first in Iran's history.

In announcing his withdrawal today as a candidate, Farsi, a college professor who advocates strong Islamic influence on the government, said that he would drop out because of questions about his nationality.

Farsi, 47, who was the nominee of most clerical groups and the powerful Islamic Republican Party, revealed that his father held Afghan citizenship. This apparently disqualifies him under the constitutional requirement that presidents be "Iranians by origin."

Although Farsi failed immediately to throw his support to another candidate, much of his influential religious backing is expected to go to Minister of Economic Affairs and Finance Bani-Sadr, who was the mosques' early favorite.

The other strong contender in the field of 101 presidential candidates is Ahmad Madani, 51, the recently resigned Navy commander and governor general of oil-rich Khuzestan Province, who has little support among religious groups.

Backing of Iran's various theological societies and Moslem leaders is considered very important in a nation swept by Islamic fervor and virtual idolatry of the revolutionary leader and father figure, Ayatollah Ruhollah Khomeini.

As a staunch proponent of radical Islamic economics, Bani-Sadr, 47, pleased the important religious hierarchy by nationalizing banks and abolishing interest on some loans -- a policy consistent with the Moslem ban on usury.

The French-educated economist spent 15 years in Paris exile before the clergy-led revolution toppled Shah Mohammad Reza Pahlavi last February.

Bani-Sadr is deeply suspicious of the United States, which he blames for most of Iran's troubles. But he has forcefully advocated a quick end to the hostages issue -- not necessarily on U.S. terms -- while other national leaders procrastinate over the possibility of spy trials, international tribunals or partial releases.

Appointed acting foreign minister in the initial weeks after the Nov. 4 embassy takeover, Bani-Sadr was fired by Khomeini after he was accused of being "soft" for suggesting that he plead Iran's case before the U.N. Security Council.

Although presidents serve at the pleasure of the nation's top theologian, who is presently Khomeini, domestic and international conditions have changed so radically in recent weeks that Bani-Sadr might have a freer hand in the hostage crisis if he were elected.

Nevertheless, any solution would have to be cleared by the radical embassy captors, who have physical control over the hostages and favor Farsi because of his ardent support of their activities and his Islamic militance.

The embassy captors, who describe themselves as Islamic theological students, have shown no sign of softening their demands. In recent interviews, they have espoused the same rhetoric as they did 10 weeks ago.

Diplomatic sources here believe Iran's government has sought to cut off the captors from American reporters because press accounts give the impression that the young militants run the nation's foreign policy -- and that this complicates negotiations.

Foreign press coordinator Sadegh, in an interview today, said the expulsion of American journalists could make the captors "more relaxed. It probably will affect [the hostages] positively."

American correspondents, ordered out on grounds that they distorted the news by giving undue attention to the embassy detentions, spent much of the day trying to determine details of the exit order.

In the first full explanation for the press ouster, which includes this correspondent, Sadegh recited the now familiar list of complaints -- chiefly that U.S. journalists ignored past Iranian sufferings, which are cited here as justification for holding the hostages.

Saying the American press overlooked the "crimes of the shah" and American support of his rule, he accused reporters of fostering an atmosphere in which "the people in the U.S. are in an uproar against Iran." a

"The American people have been led to believe this was done in contrast to international law," Sadegh said. "That has taken the focus away from why such action was taken, which from our point of view is a lot more significant." s

Americans "would be in an uproar against the United States if they knew what was paining this country," he continued. "When the reports here result in the kind of reaction against [Iran] that is totally out of character with the compassionate people [of the United States], then I think the media is not doing its job."

Sadegh cited several recent television broadcasts and newspaper articles -- including a Washington Post editorial critical of earlier Iranian press crackdowns -- as examples of misguided reporting.

Although he held open the possibility for a return of American journalists, Sadegh said that "neither we nor the United States are benefiting at this time." He suggested that Americans could get their news from European news agencies.

Meanwhile, an English-speaking newspaper, the Tehran Times, reported that Baluchi tribesmen in southeast Iran are providing a safe harbor and materiel aid to Afghani rebels fighting Soviet troops in their country.

The newspaper quoted Baluchi leaders as saying that the Afghanis cross over the border to Iran each night and receive food, medicine, money and guns to continue their fight.

Although the Baluchis of Iran, have been aiding Afghnistan's Baluchis since the first pro-Soviet coup in Kabul in April 1978, such information was not published here before.