James M. Stone, chairman of the Commodity Futures Trading Commission during the Carter administration, packed his bags last January and resigned from the five-member board.

On May 1, Philip McBride Johnson resigned as chairman, after giving the Reagan administration nearly four months' notice so it could find a replacement.

Even so, the White House hasn't found a replacement for either man. The agency is operating with the minimum of three commissioners, one of whom, Susan Phillips, is acting chairman.

Several names have surfaced as potential appointments, including former representative Robert D. Price (R-Tex.), who was first elected to Congress with Vice President Bush in 1966. But Price appears to be out of the running now.

"I don't know what's going on at the White House," said a government official who is close to the CFTC. "I guess they think it's a little, out-of-the-way agency that nobody is too concerned about."

If that is the case, the Reagan administration would not be the first to take the nine-year-old agency's personnel problems less than seriously. At no point in the Carter administration did the commission have its full complement of members.

Nevertheless, it continues to make important decisions that affect both commodities trading and the way commodity brokers and customers deal with one another.

Last month, for instance, the three commissioners approved a controversial rule that permits brokerage firms with customers who trade in the futures markets to include a clause in their contracts that requires most disputes with those customers to be settled by arbitration, restricting an unhappy customer's ability to go to court.

The same brokerage firm cannot put such a clause in a contract with customers who buy stocks and bonds, under Securities and Exchange Commission rules.

This week the commission approved a new futures contract, in potatoes trading, that changes the way such contracts are settled.

In a futures transaction, one party agrees to deliver a certain quantity of a product--it might be grain, metal or Treasury bills--at a specified price and date. The other agrees to buy the product at that date and price.

Normally most of those contracts are settled in cash. Few participants in futures transactions really are interested in buying or selling the commodity involved. They are interested in speculating (making money off price changes) or in hedging their risk. But either party can demand that the commodity actually be delivered rather than settling in cash.

This week, however, the agency approved a contract that permits settlement to be made only in cash--making it almost impossible for someone to "corner" the market in a commodity.

To corner a market, an investor or group of investors buys enough futures contracts requiring delivery to ensure that on the settlement date there is not enough of the commodity available to fulfill the outstanding contracts. When the investors demand delivery rather than accepting cash, the price of the commodity rises sharply as those who promised delivery scramble to find enough of the commodity to fulfill the contracts.

Some analysts worry, however, that a cash-only contract removes the futures market from any real relationship to the underlying commodities. These contracts may so change the way the futures markets work that grain processors and others who use the markets to hedge may have difficulty using them in the traditional way.