Israel Cohen, the 72-year-old president of Giant Food Inc., has put $6 million worth of his Giant stock up for sale and says he would be willing to discuss selling the company if someone came along and offered him $1 billion.

"I used to say, 'Never, never,' " said Cohen; "I don't say that anymore. If someone came along and offered the right kind of price -- 20 times projected earnings -- it would be foolish not to discuss it."

Investment specialists who follow Giant expect the supermarkets to earn about $1.70 a share in fiscal 1986. Those earnings, multiplied by a factor of 20, would equal $34 a share. With 30 million shares outstanding, that would be equivalent to a price of more than $1 billion.

Of the $1 billion figure, Cohen said, "You couldn't replace Giant facilities for that."

Cohen, in a telephone interview, appeared to be edging closer to the idea of eventually selling Washington's biggest supermarket chain. In February, Cohen said that, with a major expansion program underway, "now certainly wouldn't be the time" to consider a merger or possible acquisition.

Cohen's key motivation for selling, it appeared, would be the need to raise cash for estate-planning purposes. While Cohen would pay capital gains tax on any profits from the stock, the sale would provide cash for any future estate taxes that would be levied.

The Giant Food chairman owns 1.64 million shares of the nonvoting Giant stock that is traded on the American Stock Exchange. All 250,000 shares of voting stock are owned by Cohen and Charlotte Lehrman, wife of Giant's cofounder, Jac Lehrman. Each owns half of the shares that control the company.

In recent weeks, Cohen began the process of raising cash by notifying the Securities and Exchange Commission that he intended to sell 296,000 shares of his nonvoting stock at $21 a share, which would total $6.2 million.

"I'm buying a condo, I have a place in Florida. And," he added with a laugh, "I need some cash to operate in the style to which I've become accustomed."

Cohen said he plans to buy a $750,000 condominium in the new Somerset House building planned on Wisconsin Avenue opposite Saks Fifth Avenue in Chevy Chase.

His stock sales have been delayed, however, by an uncooperative market. After he sold about 25,000 shares at $21 a share, he said, the price dropped. It closed yesterday at $19.63 a share. Cohen said he told his broker to stop because he didn't want to sell at less than $21.

Eliot H. Benson, director of research for Ferris & Co. of Washington, said that while $1 billion might seem high by industry standards, it was not out of line. "I can clearly see someone willing to pay that kind of price," he said. "It would not be excessive for what they would get in return -- a substantial organization with skills and talents that could be used" in another supermarket business.

Thomas T. Taylor, president of Offutt & Taylor of Baltimore, said he thought the projected price was too high. "I think that kind of valuation is more than people would pay. I think that is a couple years down the pike."

Cohen said Giant has not been seeking offers for the company. He noted that a Boston organization had approached Giant with a leveraged buyout offer, but that Giant officials were not interested. In a leveraged buyout, a company is bought with money borrowed by using the firm's assets as collateral.

The firm that has figured most prominently in speculation about a possible acquisition is Supermarkets General, operators of Pathmark Supermarkets, based in New Jersey. The two companies have discussed the possibility of Giant manufacturing grocery products for Pathmark. Supermarkets General offiicals could not be reached for comment yesterday.

Supermarkets General reported sales of $4.3 billion for the fiscal year that ended in February. Giant reported $2.1 billion in sales for the same period. Benson said the two firms would match geographically.

Although Cohen talked in terms of a price tied to 20 times 1986 earnings, that is far above the current relationship between the price of supermarket stocks and earnings. Giant stock now sells at 12.5 times annual earnings, while Supermarkets General sells at 13.7, Safeway at 10.7 and Kroger at 13.

Giant stock, which recently was split 2 for 1, sold as high as $43.50 before the split. It has moved up rapidly since last fall, when it sold around $23 to $24.

Giant plans to open about 23 stores in the next 36 months, according to its annual report. Giant currently has 134 supermarkets. CAPTION: Picture, Israel Cohen . . . puts $6 million in stock on market.