The deadline was the day before yesterday, Price-Waterhouse is hard at work, and it won't do any good for the Oscar nominees to take out any last-minute "for your consideration" ads. But one guy who figures to be well represented at next Monday's Academy Awards is taking out a splashy advertisement for himself this weekend: Oscar, for the first time ever, will do a little preceremony grandstanding, in the form of 16-page supplements delivered to 10 million readers of 19 newspapers around the country, including The Post.

In the past, the academy has shied away from any sort of self-promotion -- partly because it hardly needs any more publicity than the Oscars already receive. But the organization changed its mind this year when the North/South Communications Co. made an attractive offer: complete control over the editorial content of the supplement, all printing and insertion costs borne by North/South and a 5 percent cut of the revenue generated by ads in the supplements. The academy also stands to profit from a coupon offering special Academy Awards posters at $15 each. The noncommercial side of the inserts will include bios of the nominees, an Oscar quiz and a replica of the official ballot.

Come Monday night, the red lights to keep last year's acceptance speeches to a minimum probably won't be used. It seems everybody thought last year's show was a bit too efficient, so things should be marginally looser this time around; at least that's what the nominees were told when they showed up at the fifth annual -- and the best attended yet -- Nominees Luncheon a week ago. Woody Allen's 'Purple' Reign

The British version of the academy beat its American counterparts to the punch early this week, handing out the British Academy of Film and Television Arts Awards. But the winner wasn't 1986 Oscar nominee "Witness" or top-grosser "Back to the Future"; it wasn't even two other previous Oscar winners, "Amadeus" or "A Passage to India." Beating all four of those films was a movie not even nominated by the American academy, Woody Allen's "The Purple Rose of Cairo."

One final Oscar note: Everybody's wondered just how much the Best Picture Oscar is worth to a movie at the box office, and Hollywood business columnist Martin A. Grove has compiled figures and decided it's worth $5 million to $10 million, depending on how much money the film has made and how widely it has been exposed before the win. His figures say "The Color Purple" and "Out of Africa" stand to increase their gross by 20 percent to 25 percent if they win -- and that the other three nominees could stand to reap even bigger benefits. There's one catch, though: "Prizzi's Honor," "Witness" and "Kiss of the Spider Woman" all have been or will soon be released on videocassette, which means that instead of the $10 million more in ticket sales, they'll probably just get rented more often. The film studios, of course, don't get any share of that rental charge. Who's Going to the Movies?

The studios' biggest problems have nothing to do with who wins or loses at the Oscars Monday. Of far more concern is a three-year survey commissioned by Columbia Pictures Industries that examined the entertainment habits of 12,000 families for three consecutive Septembers.

The results may be sobering to studios still congratulating themselves on the good business so far this year: Three-quarters of those questioned, for example, didn't see a single film during any of the surveyed months. And filmgoing is rapidly becoming less and less popular -- among 10- to 19-year-olds questioned it dropped a remarkable 23 percent during the past three years. Only one age group goes to more movies now than three years ago, according to the survey: The over-50 crowd attended 11 percent more films in 1985 than in 1983.

Mostly, though, the survey makes things look pretty dismal. One industry response was suggested last Friday to the board of governors of the National Association of Theater Owners: Columbia Pictures executive Peter Seeley proposed a generic "Go Out and See a Movie" campaign, similar in execution to the campaign promoting Florida orange juice.