Soviet authorities have suddenly levied new taxes against American firms operating here as part of a package of extra hard currency payments being demanded of all foreign businesses with permanent representatives here.

Amid rumors of worse to come, the extra payments include doubled rents, mandatory extra money for local Soviet employes, and unique yearly "maintenance" charges for rented offices.

In addition, the Soviets have interpreted the 1973 Soviet-American tax agreement as empowering Moscow to levy a new tax on all profits made by American firms selling equipment or other goods to the Soviets. Soviet tax officials in late December sent letters demanding by Feb. 1 detailed company information for 1979, the peak for bilateral trade. The authorities have refused to disclose what tax rate will be used, but the worst of the rumors circulating here within the enraged U.S. business community sets the new rate at 40 percent of all Soviet-based profits.

The 28 permanent U.S business and bank representatives here have just come off the worst yearly drop in Soviet-American trade in the decade since detente brought the businessmen flocking here in search of vast new markets. That early promise never panned out, and U.S.-Soviet trade has always languished toward the bottom of both countries' trade figures.

But in 1979, bilateral trade topped $4.5 billion, and until the Soviet invasion of Afghanistan in late December that year, seemed to have achieved a breakthrough that could only mean much, much more to come. However, the Carter administration's subsequent economic sanctions shattered such notions. In 1980, trade plunged less than half the figure of the previous year. Few firms with offices and staffs here are thought to have made a profit last year, though such information is a closely guarded matter with almost every representative.

The new Soviet charges may raise the annual $300,000-to-$500,000 average cost of maintaining an office here by another 15 to 20 percent, several businessmen estimated. That could push some of them to pull out after years of disappointments in a marketplace buffeted by international political crises and Soviet reluctance to spend hard currency.

The new payments, which are being appealed to senior Soviet officials, seemed designed to increase the hard currency income from the businesses.

"They see a multi-billion dollar multinational and think it's a pot of gold," one angryU.S. representative said. "They aren't sophisticated enough to realize Moscow offices are accounted for out of Dusseldorf, Vienna or London, and we have to show black ink like every other part must show it."

No other major capitalist country faces the kind of profits tax the Soviets want to impose, and the U.S. firms have asked the State Department for advice and help in fending off the sudden charge. The Soviets have demanded such information as to how much a firm paid for raw materials it used in manufacturing items later sold here. "Absurd," said one source. "I don't know whether they're just stupid or just evil-minded."

In part, the new payments call for reasons other than cost. They represent new Soviet attempts to play a role in the operations of firms here, which already are required to file detailed reports of all business contacts and travels they make in the country.

Instead of paying their local employes directly, the firms as of April 1 will be required to deposit money in an account with the government organization which caters to all foreigners permanently resident in Moscow, the Diplomatic Service Corps Bureau. The bureau will then pay the employes, virtually guaranteeing endless paylines and lost work-hours. In addition, the bureau has demanded an extra monthly 10 percent "social welfare" payment, and deposit 2 1/2 months' salary ahead of time in a noninterest bearing account "in case of salary disputes."

So far, these new regulations apply only to foreign businesses, but the foreign diplomatic and news community has been awash in rumors for months that they, too, may eventually face the same new demands.

These rumors also say that foreigners in the months ahead will be denied the access they now have to special coupons, or a form of money available only to those with hard currency accounts. The coupons can be used in special food, clothing, and appliance stores where, apart from moderate prices, the selection is wider and more dependable than in regular stores.

Some foreigners here estimated their operating costs for such items as business entertainment could triple if the coupons disappear.

The tough new demands for more money have been matched by increasingly aloof attitudes of Soviet trade officials toward the Americans, some sources report. While a number of firms continue to land contracts for new equipment or spare parts, others find themselves increasingly in the deep freeze.

Two representatives are said to have been WAITING SINCE october to see some Soviet officials, and others say the Russians may be coming to the view that they do not need the Americans much after all -- Moscow can get what it needs from the Europeans or Japanese.