Rad Car, Brainoed-Out Driver : HOLLYWOOD DAYS, HOLLYWOOD NIGHTS The Diary of a Mad Screenwriter<i> by Ben Stein (Bantam Books: $7.95; 224 pp.) </i>

Why does Ben Stein want to tell us these things?

Stein, Yale Law School graduate, former Nixon speech writer, former Wall Street Journal columnist and current screenwriter, keeps a journal. It’s now published as “Hollywood Days, Hollywood Nights: The Diary of a Mad Screenwriter,” so we all can read it. But there are some things we would be better off not knowing. The question remains: Why is Stein doing this?

This also seems to be what Stein is asking himself about his own life. Periodically, he ruminates about how important Hollywood is, how movies “have a power as great as human imagination.” He talks about how the movie business “is a launching pad into the realm of anything can happen. It is a Cape Canaveral for trips into a new, wildly bigger, more important, more powerful you.” But this all sounds as if he has to rationalize what he is doing in Los Angeles. He shouldn’t waste his time. As detailed in his diary, his life reads almost like a caricature of the worst aspects of Hollywood.

This is revealed in more than his effusive use of adjectives. It seems to go far deeper. For example, he has a drop-dead Porsche. Perfect, except that it is a financial black hole, endlessly absorbing money--the brakes have had to be fixed 10 times over two years; his radio is repeatedly stolen. So why does Stein keep a car that he admits he loathes? Because “There is no Toyota ever made which would get two teen-age girls in miniskirts to run over and flirt with a brainoed-out 41-year-old.” When “two beautiful girls” admire his car as he drives along Mulholland Drive, and one calls out a compliment, Stein pulls over to talk.

Much of Stein’s life, in fact, seems to be spent in the company of beautiful and amazingly stupid girls he has picked up along the way. He meets one young woman, Stacey, on a plane to Santa Cruz. She is “a beautiful girl with green eyes, curly brown hair, and a sweet, childish pout. She also had a chest that would make Hugh Hefner have a second stroke.” She also does not know what Wall Street is or the difference between “Washington, D.C. and Washington state.” When she gets back to Los Angeles, Stein takes her to lunch at Mr. Chow. She ultimately becomes one of his two “closest friends in the whole world.”

In the same fashion, Stein becomes close to a high school girl, Tammie, when he writes about attending courses there. As he explains it: “I am standing there with a cute little 5-foot-tall pixie with black hair who listens carefully to every word I say.” Over Easter vacation, he calls her up and takes her to dinner at Morton’s, also to Spago. She meets Sylvester Stallone, and she tells Stein: “This was the best dinner I’ve ever had. I would love to come back here.” He would love to take her.

In addition, he spends much time with Sara, who works for him and is “so beautiful that men literally walk into the wall staring at her, and women visibly grimace at her youthful perfection.” She has never heard of World War I, World War II or the entire nation of Korea.

Then, of course, there is Marcie, who serves as a sort of leitmotif since Stein runs into her repeatedly. She says things like: “I don’t want a man to take advantage of me, no matter how available, how ready I may look. After all, I’m only 14. . . . That means don’t touch. . . . Not unless you are willing to get to know me.” Whenever he sees her, Stein has time to chat.

So, what is going on here? Stein admits his wife, Alex, “has been convinced that I am completely insane for a long time now.” He insists that through friendships with Stacey and another young girl, “I have gotten at least five development deals from them and a reputation as a man who is hip to what kids want to see and know, which is worth having in the picture business.” But with all these “children,” as he calls them, so horrifyingly stupid, how can he spend so much time talking to them? And with his reputation for understanding the youth market, why is he having so much trouble setting up a deal?

When he is not dallying with children, Stein does have some insightful things to say about Hollywood. He explains why a studio development executive has an almost all-consuming desire to say “no.” He tells how, for a cameo role, his description of the Smoot-Hawley tariff bill and the Laffer curve sends an entire film set into gales of laughter. (A story that appeared in a better form on a newspaper Op-Ed page.)

At one point, Stein is pitching his “favorite” screenplay, “My Grown-up.” The studio executive is appalled: “You mean that thing about the congressman having an affair with a college girl. That was sick. That was a really sick idea.” Stein defends it by comparing the story line to “Lolita”--which, of course, the executive has never heard of. I’m sure that Stein wanted that anecdote to illustrate the problem with studio executives. But it really says much more about Stein.