Two friends of mine were engaged in an animated conversation. One, unmarried, is perhaps 25. The other, married, may be over 40.

The married man said, "Don't be so stubborn. Take her out to dinner."

"No way," said the unmarried one. "No way."

"What are you afraid of?" persisted the older man. "Just because you take a girl out to dinner doesn't mean you have to marry her."

"Oh?" responded the younger man archly. "How did you meet your wife?" The other man looked down at the floor. "I took her out to dinner," he said softly.

"Aha!" the bachelor cried triumphantly, and thereupon the conversation came to an abrupt halt. But if that young fellow thinks he's going to escape matrimony forever he's not taking into account today's topsy-turvy sex roles. Some day a young woman is going to take him out to dinner, and then we'll find out how resolute he really is. INVESTMENT NEWS

Many advertisements that offer gold coins for sale imply that buying such coins is an almost certain way to reap big profits. They use terms like "rare opportunity," "for a limited time only," and "hedge against inflation."

The Soviet Union is currently running ads in this country offering to sell us "Chervonets." The ad says:

"Currencies jump up and down wildly . . . . But throughout the century, gold has generally maintained its purchasing power."

The implication is that although the dollar fluctuates in value, the price of gold does not. The truth is that the price of gold has been bouncing around like a yo-yo. Daily fluctuations in the value of gold are many times those of the dollar.

The ads say the Russian gold pieces are sold by coin dealers, but the dealers I called were almost unanimous in saying they don't care to handle the coin. At Deak-Perera, for example, I was told, "It's not a good investment, and we just don't like to see our customers send American dollars over to Russia for this kind of thing. There are much better ways to invest in gold."

One dealer (Central Maryland Coins) said he had one Chervonet in stock. Its price: $130.

The Russian ad says the Chervonet contains "1/4-fine troy ounce of gold," but it also gives the "fine gold content" as "7.7423g." That puzzled me for a while because I was familiar with a troy scale that calls for 24 grains to the pennyweight (dwt.) and 20 dwt. to the troy ounce. While researching today's column I learned from Gene Riffle of the Maryland Coin Exchange that the abbreviation "g" stands for grams as well as for grains, and that there are 31.1 grams to the troy ounce. So 7.7423 grams would be almost but not quite one-fourth of an ounce of gold.

When gold is selling for $400 an ounce, one-fourth of an ounce would be worth $100. One who pays $130 for a Russian gold coin that contains just under one-fourth of an ounce of gold gets no bargain.

Coins offered by private mints contain an even smaller percentage of gold. Example: The Historic Providence Mint recently advertised a "miniature $20 gold piece" for "only $20." There was no mention of the gold content of the coin, so I called the number in the ad and asked the question.

"I'm sorry, sir," was the answer, "but we do not have that information here.

We're just order takers."

"You're an answering service?" I asked. She said yes. "Where can I call the company itself?" She didn't know.

I obtained the number and called Rhode Island. "The coin contains .5 pennyweight," I was told.

Half a pennyweight is one-fortieth of an ounce. One-fortieth of $400 is $10. But the Historic Providence coin is not pure (1000 fine) gold. It is 900 fine (sometimes called 22-karat), so the gold in that $20 coin is therefore worth only 90 percent of $10, or $9.

When this point is raised, private mints reply, "Oh, the value of the gold is only part of it. This is a collector's item, an art object, a rarity. Because of its beauty and rarity, it will appreciate in value as time passes." b

Perhaps. But in that case it ought to be advertised as an art object, not as an excellent way to invest in gold.

Postscript: All gold coins sell for a premium above their gold content. The larger coins sell for at least 8 percent more than their gold value. On smaller ones, the markup is much higher. An American $20 gold piece, which contains a shade under one ounce of gold, sells for between $450 and $600 today, depending on its condition. "Uncirculated" $20 gold pieces sell for $700.

I have used $400 as a benchmark price for gold although gold is a bit less than that as I go to press. When "spot" gold prices go up or down, coin prices also fluctuate. So before you invest, make sure you know what you're doing. Buying coins is not necessarily the best way to invest in gold.