The Commodity Futures Trading Commission ordered trading in the March wheat futures contract suspended today on the Chicago Board of Trade, the second such action taken in the commodities market in a week.

The CFTC used its emergency powers Thursday night because it said a few speculators held futures contracts calling for delivery of more wheat than is currently available. In addition, a significant shortage of transportation and warehouse space exists in the Chicago area.

These factors are creating a major market disturbance, the commission said, preventing the market from accurately reflecting the forces of supply and demand.

Among the many possibilities available under the Cbot/'s self-regulatory responsibilities, the exchange could require liquidation of the long, open positions or require that a percentage of them be sold off each day, said William J. Monahan, of the Cftc/. In this case, a long position is one requiring delivery of wheat after March 21.

In its order, the commission said that information acquired from cash grain merchants and other sources indicated:

A small number of wpeculative traders has established and is maintaining a large, potentially dominant, long, open position in the March wheat contract.

Although only four trading days remained before expiration of trading in the conrtact (March 21), the group of traders is continuing this action while other traders in the contract are reducing their long, open positions.

The combined open interest of these long speculators is more than 80 percent of the total open interest in the wheat contract, the CFTC said. The commission would not give exact figures on how much wheat was involved.

These combined positions substantially exceed the total quantity of wheat currently available to fulfill delivery on the contract.

And, the CFTC, what wheat that can be delivered is not all acceptable because of variety, grade or commitments to commercial users.

Last Friday, New York Mercantile Exchange, trying to head off a threatened collapse of the potato market, halted trading in spring potato futures.

The exchange said there were not enough high-quality Maine potatoes available to satisfy futures contracts that called for delivery of nearly 11,000 boxcars of potatoes in the next three months.

If trading had not been halted, industry sources said, potato prices on the New York exchange might have soared to $20 a hundred pounds and many sellers would have defaulted on their contracts -- a disaster for the potato market.

And in another major commodities action, the CFTC charged Tuesday that firms in El Salvador, Brazil, the Cayman Islands and New York were illigally manipulating trading on the New York Coffee and Sugar Exchange. The commission is investigating a series of attempts to manipulate coffee prices.