Beside the Oise River in this sleepy Paris suburb where Vincent van Gogh once lived, Massoud Rajavi charts the future of an Iran he says his Mujaheddin-e-Khalq guerrillas will, any day now, deliver from the chaos of Ayatollah Ruhollah Khomeini's rule-by-mullah.

The news from home has been particularly encouraging for him this week. Khomeini's authorities have announced through their own news agency that Mujaheddin youths are demonstrating in the street, openly defying the mullahs' government for the first time on a large scale and even fighting gunbattles with Revolutionary Guards in the middle of Tehran.

The announcements seem to herald a watershed in the month-long terror campaign attributed by authorities in Tehran to the Mujaheddin, but for which Rajavi -- citing his delicate position as a guest of France -- has declined to claim or deny any direct responsibility. Scores of leading Islamic politicians, including the president and prime minister, have been killed in recent bombings and assassinations in Iran.

According to Rajavi's vision of Iran's future, the teetering ayatollah will tumble soon, and Rajavi will return as prime minister to begin putting the pieces of his country back together. Beside him will be Abol Hassan Bani-Sadr, the deposed president who with Rajavi fled to exile July 29 and formed the National Resistance Council, whose seat -- but only for the moment -- must be Auvers-sur-Oise, 30 miles northwest of Paris and 2,000 miles from Iran.

"There is not any other alternative besides us," Rajavi said confidently in an interview. "You Americans should be especially careful in this. You were wrong once before, you remember."

There is no way to judge the accuracy of his assertions. Iran is closed to most foreign correspondents. What information gets out comes almost exclusively from the Khomeini government's radio, the Voice of the Islamic Republic, and the news agency, Pars. But Rajavi, 34, appears to have no doubt that he is on his way back "soon, very soon" to help rule Iran, and for two hours he explains to a visitor why he is so sure and what he will do when he gets there.

Rajavi, with intense, dark eyes and a thick, black mustache only partially covering a scar on his left cheek, received visitors wearing a well-tailored gray suit and a blue shirt open at the neck. In a soft, well-mannered voice, he explained his goals point-by-point in serviceable English. A political science student at Tehran University, Rajavi became involved in the struggle against the shah early on and learned English in his cell during imprisonment for underground activities.

Rajavi is guarded in describing what Iran would be like under Mujaheddin rule with Bani-Sadr as president and himself as prime minister, but he insists that it would be independent of the Soviet Union and the United States. Although Bani-Sadr was elected overwhelmingly as president and is better known than Rajavi, the Mujaheddin leader speaks with the confidence of someone in charge.

"We will have a free general election," he said. "The people must decide about their new constitution and their new president."

The government, he said, will be "national, democratic and Islamic."

"We will be respectful of private ownership in this period," he added. "We must accept -- we have accepted -- a national bourgeoisie. But of course, it doesn't mean it will be unleashed."

In what seemed to be carefully wrought terms, Rajavi described how the Mujaheddin propose to solve the turmoil caused by drives for increased autonomy among Iran's minorities in Khuzestan, Azerbaijan, Kurdistan and Baluchistan. Although overshadowed recently by war with Iraq and chaotic antigovernment violence, autonomy demands have been a major threat to the Khomeini government.

"Under the framework of a united Iran, under the framework of national integrity of a united Iran and the national sovereignty of a united Iran, we recognize internal administrative autonomy," Rajavi said.

The war with Iraq, he added, can be solved by negotiations once Khomeini is gone. Although he condemns Iraq's attack on Iran nearly a year ago, Rajavi said the underlying cause of the dispute was Khomeini's "provoking" Iraq by trying to "export" Iran's Shiite Moslem revolution to the Shiites of Iraq, who live under a Sunni Moslem government.

A new government led by him and Bani-Sadr, Rajavi said, would pledge to keep out of Iraqi affairs. Once this is established, he added, negotiations could overcome disputes about access to and sovereignty over the Shatt-al-Arab waterway that has been the war's main theater and territorial bone of contention.

Rajavi said those who backed the shah and those backing Khomeini now would not be executed or imprisoned. Instead, they would be sent to universities for "popular education."

"We are not Pol Pot," he says, referring to the mass killings in Cambodia. "Our policy is not killing everybody. We must try to renew them, to change them. We must invite them to the university, a training university. They calm their guilt."

As he outlined his goals, Rajavi referred to handwritten notes to make sure he forgot nothing of the message that he says must go out to the Americans, who are wrongly convinced, he fears, that without Khomeini Iran would face a bloody civil war opening the way to intervention by the neighboring Soviet Union.

"Be sure that after Khomeini you will not have civil war or bloodshed," he said. "Do not think that after Khomeini there would be a power vacuum."

Nor would there be a military coup, he added, because the Army as it stood in the shah's days is "beheaded" and a growing number of officers have "popular tendencies" favorable to the Mujaheddin. Moreover, he insisted, "the anarchy of Khomeini" has reduced the Army's ability to act as a unit.

Instead, the Mujaheddin-e-Khalq, or People's Strugglers, will inherit power because, in Rajavi's portrayal, they are the only group with broad popular following, political and military organization and a clear idea of what it wants to do.

"There are some other organizations," he says, "but not popular ones. We are the only popular organization."

Rajavi refused to reveal the number of armed Mujaheddin guerrillas but claims their followers include "millions" of Iran's 35 million inhabitants. French diplomats with experience in Tehran estimate the Mujaheddin's armed strength at between 20,000 and 25,000 and the number of their supporters at half a million.

To dispute these estimates, Rajavi underlines that by the Khomeini government's own count, more than 1,000 Mujaheddin have been executed since June and more than 10,000 are in prison. Nine months ago, before Iran's terror and execution campaign made distribution impossible, the group's newspaper had a circulation of 500,000, compared to the progovernment Islamic Republican Party paper's 30,000, he said.

The Mujaheddin organization includes a Central Committee and a broader Central Council, with authority flowing from the committee through the council to numerous cells around the country, particularly in northern Iran near the Caspian Sea. Diplomats who have studied the group say it is well-organized but acknowledge that it is hard to tell how well it has survived the recent increase in executions -- or indeed whether all victims identified by the government and claimed by Rajavi as Mujaheddin actually were.

"So far, we have not had a strategic shock," Rajavi said, while admitting that the executions have taken a toll. "Not one from our Central Committee or Central Council" has been executed.

Western diplomats who served in Iran describe the group as tough, determined and ruthless. It has been struggling since the mid-1960s, and its members were those who actually went into the streets with guns during the violent phase of the revolution that drove the shah from power, they say.

The late shah, Mohammad Reza Pahlavi, called the Mujaheddin "Islamic Marxists," a term that has remained with them, to Rajavi's irritation. "We are not Marxists; we are true Moslems," he said.