A close adviser of Ayatollah Ruhollah Khomeini has proposed a series of drastic economic changes for Iran's proposed new Islamic republic that include the cancellation of the country's foreign debt and a curtailment of its oil production by 60 percent.

The economic pronouncements of Abdolahassan Bani-Sadr, who returned here from exile with Khomeini last week and who reportedly has been working for several years on economic plans for the ayatollah's republic, are sending shudders through the Iranian and Western business communities here.

Iran's default on an estimated $8 billion foreign debt could produce unforeseen adverse consequences in Western financial markets. The proposed curtailment in oil production would cut sharply into Iranian oil exports, which accounted for about 10 percent of the West's oil consumption last year.

While a reduction in oil exports would presumably be covered by increased output in other oil-producing countries, the possibility of a major disruption in financial markets has produced increasing concern in banking circles.

American bankers had about $2.7 billion in outstanding loans at the end of 1978 while U.S. government credits extended to Iran are estimated at $1 billion. These figures do not include arrangements for Iran's massive purchases of military equipment in the United States.

Bani-Sadr has been widely mentioned in the local press as a a possible finance minister in Khomeini's provisional government, although some opposition sources privately doubt that.

In either case, members of Khomeini's entourage say Bani-Sadr is close to the 78-year-old ayatollah and is serving as a principal economic adviser. Moreover, none of his pronouncements have been repudiated by Khomeini or his aides.

The exact extent of Iran's debt in the United States could not be assessed because of complex arrangements involved in Iran's purchases of U.S. military equipment. The government of Prime Minister Shahpour Bakhtiar already has canceled contracts for U.S. arms valued at $8-10 billion.

Several Western European countries, and particularly West Germany, France and Britain, are known to have large financial exposure in Iran.

Businessmen and economists here say plans to repair the country's devastated economy come at a time when Iran is confronting another problem -- a food crisis in the months ahead.

Bani-Sadr's economic program also calls for the nationalization of all banks and credit systems, heavy taxes on imported spare parts, the transfer of industrial management to workers, committees in each factory and an agrarian reform to create agricultural "collectives."

In recent lectures at Tehran University, Bani-Sadr has gone even further. Outlining solutions to Iran's economic problems, he said Iran's first goal should be "to stop being a crude oil exporting country and try to establish our own independent economic institutions." In the meantime, Iran would expect higher prices for its oil, he said.

He also called for "severing" Iranian banks from the world banking system and "abolishing" interest.

The son of a Moslem clergyman and reputedly the holder of economics and sociology degrees, Bani-Sadr has said the Islamic republic's economic system would be "neither capitalist nor Marxist, nor a combination of the two."

Here are some of his views culled from his speeches and local newspaper interviews:

He favors "decreasing oil production because part of it is not really for people's consumption but just for building up reserves. Forty percent of [previous] production would be enough for present needs."

Foreign companies operating in Iran were told "thousands of times that this is an illegal regime and that the money you are taking is theft." Therefore a new government would be justified in disavowing debts incurred by previous governments under Shah Mohammad Reza Pahlavi.

Heavy taxes should be imposed on imported parts to reduce foreign purchases and cause multinationals to close down their assembly plants in Iran. Then the state could undertake, for example, the setting up of complete automobile manufacturing plants instead of the present assembly of imported components.

Faced with statements like these, many Western and Iranian economists and businessmen here don't know whether to laugh or cry.

"God help us if that's the kind of economics we're going to have," said one American analyst."The trend here is irreversible toward more expenditures. But he's talking about reducing oil production by 60 percent and cancelling foreign debt. That means you can neither borrow nor earn money. It just shows he doesn't have a grip on things."

"The idea of cancelling foreign debt sends chills down my spine," a foreign banker said just before he pulled out. Iran is getting into a situation where it may have to borrow internationally just to pull itself out of the current mess."

He added, "If you start talking about not paying off foreign debt, you're in big trouble, especially since there's likely to be a continuing revenue shortfall. If foreign debts are canceled, no entity in Iran is going to be able to get credit, and credit is needed if Iran is to carry on commerce with the rest of the world. This economy runs on imports."

Said another banker, "I shudder when I look at the things Bani-Sadr is saying." He added that even higher duties on imported parts was "a good way to stop industry altogether." The reason there is little local manufacturing of car parts, for example, is that the volume of the domestic auto industry does not justify it economically, he said.

Iran in recent years has been importing some 30 percent of its annual food needs, according to agricultural specialists, but in the last few months, strikes in the banking system, customs administration and various government bodies have curtailed some key imports. In many cases, the importing agencies have not been able to open letters of credit to pay suppliers because of the bank strikes.

Particularly acute are supplies of animal feed, of which Iran normally imports about half its needs, specialists say. As a result owners have had to start slaughtering dairy cattle and stop hatching as many layer and broiler hens.

"It's getting pretty serious," a Western agricultural specialist said. Iran has ordered enough wheat and almost enough rice to meet demand -- assuming the ships can be unloaded and the goods distributed -- but it faces shortages of beef and poultry in the coming months, he said.

A rice-consuming nation, Iran grows 750,000 tons of the grain a year and imports 450,000 tons -- 93 percent of that from the United States. Prices of this and some other commodities are government subsidized.

These subsidies and such practices as importing hundreds of thousands of live sheep a year from Australia and Romania may not be economical, an analyst said, "but if the government didn't do it, the disturbances in Tehran would have been food riots."

"In general, consumer supplies are adequate now, but I can see a crunch within a month in some commodities," another specialist said.

Said a Western banker, "The food situation is the most frightening prospect of all, even more frightening than the collapse of the economy."