"Who," you ask Margaret Truman, "would go out and buy their child a 15-inch-tall green plastic Godzilla monster doll that sticks out its ugly pink tongue and shoots off a furry claw?"

That question is asked because you're trying to provoke Truman into saying just one naughty thing about the toy industry. For the past couple of months she's been traveling about the county as a spokeswoman for the Toy Manufactures of America, who make about 90 percent of the toys we buy.

Yes, the Margaret Truman -- the author, sometimes TV personality, the president's daughter.

Her face all smiles, she's a holiday package of warmth and charm in Christmas-red dress and pearls, relaxing after a round of promotional appearances. Her answer catches you off guard; the ploy is doomed.

"Well," she says, "we got one for our two younger sons together. They liked to watch the Godzilla movies." "We" includes husband Clifton Daniel, former Washington bureau chief of The New York Times.

That, it seems, is who buys those $20 Godzillas.

But, shedding her spokesperson role for just a moment, she reveals a trace of parental exasperation. "They were interested in it for all of three days, and then they went back to the movies."

Truman's job, on a one-year contract, is to inform the public on the proper choice, use and safety of toys. She took it, she says, because a friend who is in public relations was looking for a spokesperson.

Her experience -- beyond briefings during toy-factory visits -- is that of a mother of four sons, now 13, 16, 20 and 22.

When buying a toy for a child, she advises, "Be very careful it isn't too old for them and that they can cope with it."

She recalls that her father once returned from a trip bringing her an "enormous" doll taller than she. "I went screaming from the room and never played with it."

When two sons were about 3 and 5, they received a battery-run dog that they, too, refused to play with. "My theory," she says, "is when they first saw it they thought it was a real dog," and were disappointed.

But, she adds, "My father thought it was a great toy, and kept playing with it. I had to take it away from him."

Truman suggests that relatives who want to give toys as gifts check first with the parents for ideas, or send the money to them to make the purchase. That, she says, is what her parents did because they felt they did not see their grandchildren often enough to make an appropriate choice.

The toy industry, she notes, now often specifies on the package the age range the toy is aimed at. A toy that is too old for a child can be "frustrating," she says.

To find out what her sons wanted under the Christmas tree, she and her husband "used to take our children toy-shopping with us," a practice some parents may feel is courting disaster. But "we didn't buy then, and we didn't buy them everything."

What were some of her favorite childhood toys?

Though "I was not much for dolls," she says, she did treasure a comfortable Raggedy Ann. She also still keeps "bits and pieces of a pretty little tea set" she had as a child. "We weren't allowed to have tea. They didn't think it was good for us. So my friend and I grew up on sugar and lemon water."

Once, on her eighth birthday, she had hoped to get an electrical train. Instead, the big surprise was a baby grand piano -- something of a disappointment, she says, despite her father's well-known love for the instrument.

Her sons, she says, have been partial to construction toys. "That's very common in boys." When it is suggested that might sound somewhat sexist, with Lincoln Logs and Erector sets now displaying both boys and girls on the packaging, she responds quickly that the toy industry "has made a concerted effort to keep up" with the issue of sexism.

She adds that racism is another issue that has been tackled. That WASP doll has been joined by her black, Asian and Hispanic sisters and brothers. "And it's high time, I think, don't you?"

How does she feel about cap guns or war toys? One can buy a plastic "Triple-action" M-3 machine gun for $8 at one downtown department store.

"It's up to the parents. If they don't approve, then don't buy them. One rule is that in our house they don't fire them off."

Though they're not actually toys, she likes books as gifts for children and was charmed by the remarks of one fellow talk-show guest who said such books have a double life: The first is when you read the book to the child; the second is when the child is able to read it alone.

"I know "The Cat in the Hat Comes Back' by heart. I was glad when they got old enough to read it themselves."

On her travels, which continue until mid-December, Truman is carrying a large assortment of toys, including several electronic gadgets. One called "Merlin," which she likes and which her younger sons particularly favor, plays such games as blackjack, as well as 48 musical notes. Such devices make good gifts for children old enough to enjoy them, she says.

"They're going to live in a computer world. This is preparing them for it."

Though parents may shudder at the cost of toys, she says prices in the toy industry have not inflated as rapidly as clothing and other merchandise.

One toy manufacturer, however, making a similar promotional tour for his company's plastic ski sled, is warning consumers that because of the higher cost of oil his product will go up 15 percent as reorder shipments reach the store shelves this month.

Donald Wagner, president of the Pittsburgh-based Sweco, says he expects other toy manufacturers using oil-based plastics may raise prices also. His "Big Ski," which now retails at $24 to $25, will soon go to $29.

Truman says the members of the Toy Manufacturers of America have gone to a lot of effort to build safe toys. For example, she says, in their tests they utilize a tube the size of a baby's throat. If a part can slip down the tube, the toy is rejected. Accidents do occur, she says, but often it's the case of toy being misused.

In her visits to toy plants, she saw a number of "really fascinating" things already being planned for next year -- the big wholesale push for Christmas 1980 begins as early as the February trade shows -- but she was sworn to secrecy.

As for that longed-for train set that she never got for her birthday, a toy maker heard her story this year and sent her one.