Iranian Finance Minister Abol Hassan Bani-Sadr, apparently headed for a landslide victory in the nation's first presidential election, said yesterday that the 12-week American hostage crisis is a "minor affair" that could easily be solved.

Bani-Sadr failed to outline his conditions for any hostage release but, when he served briefly as foreign minister last November, he was said to be pushing for U.S. approval of an international investigation of the alleged crimes of the deposed shah, Mohammad Reza Pahlavi.

In an interview with the Paris daily newspaper Le Matin, the French-trained economist also said Iran is ready to provide military assistance to Moslem rebels in the neighboring Afghanistan who are fighting the Soviet invasion of their country.

Unofficial election results, with nearly 30 percent of the vote counted, showed Bani-Sadr had three times as many votes as the other seven top contenders combined. "I've definitely won," he declared, and took advantage of his new forum to make important foreign policy pronouncements.

Claiming victory on election night Friday, he said his first priority as president would be settling the hostage crisis. In yesterday's interview with Le Matin, he suggested that releasing the estimated 50 Americans need not be a complicated matter.

Although an ardent foe of American influence in Iranian affairs, Bani-Sadr, 47, has long favored an early end to the occupation of the U.S. Embassy in Tehran, which he has called a misguided venture that distracts the nation from pressing economic problems.

"With regard to the United States, there are many problems," he was quoted as saying. "But the affair of the hostages can be solved almost naturally. From the moment when the people give me their confidence, there will be no major difficulties because this is a minor affair."

Any decision to free the hostages would have to be cleared by Ayatollah Ruhollah Khomeini, the nation's ailing revolutionary and spiritual leader, who has the power to dismiss the president and is the only Iranian figure with influence over the Islamic militants holding the Americans.

Khomeini, 79, was hospitalized last week for treatment of heart trouble. He was visited yesterday by two Swiss specialists who reportedly diagnosed his condition as good and approved the approach of his Iranian physicians.

Although Khomeini fired Bani-Sadr as foreign minister last November for appearing too soft on the hostage issue, many believe that the Soviet invasion of Afghanistan and deepening regional and economic problems have changed official views on the need to solve the crisis.

Meanwhile, the militant youths occupying the embassy -- who have repeatedly blocked past efforts to negotiate release of the hostages -- seemed to take exception yesterday to Bani-Sadr's prediction that the crisis could quickly be settled.

In a statement broadcast over Tehran Radio, the radical captors insisted that the United States -- not the Soviet Union -- was Islam's "enemy number one" and reiterated their familiar stand that the hostages would not be freed before the ex-shah is returned to Iran.

For the past two weeks of presidential campaigning, the hostage issue has taken a backseat to Iranian electoral and domestic concerns. Most diplomatic observers believed that Iranian authorities would not turn their attention to the issue until the nation elected a president, a process that theoretically could last another two weeks if the failure of any candidate to win a majority necessitates a run-off election.

As election returns continued to stream in last night, however, a run-off appeared increasingly unlikely. The finance minister pulled farther ahead of his closest rival -- former naval commander Ahmad Madani, the favorite of Iran's middle class, who was receiving just a fifth of Bani-Sadr's votes.

By nightfall in Tehran, interior Ministry officials said they had counted 6.7 million votes -- out of a possible 22 million ballots cast by eligible Iranian men and women 16 years of age or older. Bani-Sadr won more than 5.1 million of the votes counted.Although unofficial returns were released by the Interior Ministry, a final result will not be made official until at least Monday.

A surprisingly poor showing was recorded by Hassan Habibi, the spokesman for Iran's ruling Revolutionary Council who had the backing of the nation's influential clergy groups. He was listed third in the balloting with just 3 percent of the vote.

Habibi, who became the clergy's candidate only after their original favorite dropped out of the race, was believed to have been hurt by the backing of Iran's Tuden (Communist) Party, which said it supported the candidate deemed closest to Khomeini.

Khomeini avoided endorsements for any of the eight major candidates, even though he has the power to screen contenders for the race and the authority to veto the election if he is not satisfied that the winner would conform to Islamic principles.

Although Khomeini can fire the president once he enters office, the man who fills Iran's highest elective office for the next four years will have significant powers to nominate the prime minister and sign treaties.

Bani-Sadr, a prolific writer of books and essays, is known as the theoretician of the Islamic revolution that toppled the shah last February and ended 2,500 years of monarchy. He is deferential to the nation's religious leaders, but advocates a civilian-run government.

As the chairman of the Revolutionary Council's economics committee, he helped bring about nationalization of Iran's banks, insurance companies and some industry. Later as finance minister, he abolished interest on housing loans, replacing it with service charges.

In foreign policy, he advocates steering a clear path between the two superpowers. Although he is a fierce critic of the United States, he was the first candidate to warn about the possible threat to Iran of Soviet military intervention in Afghanistan.

In his Le Matin interview yesterday, he noted that Iran feels the Soviet danger. He said, "Faced with the Soviet Union, we will aid the Afghan people with all means possible in Iran, including military means. I hope the Russians will be prudent.

"They have already lost their image in Iran, where no one believes anymore in noninterventionism."

Running a Westernized campaign staffed with young canvassers, Bani-Sadr crisscrossed the nation advocating his unique recipe for revitalizing the Iranian economy on the basis of Islamic law and radical economic principles.