The Illinois entry-level portion of the 1985 North American Scrabble Open will be held this weekend. (See accompanying story for details). In years past, the biannual North American Scrabble competition was limited to members of Scrabble Crossword Game Players Clubs, but this year anyone can enter.

Winners at the entry level will advance to semifinal competition in April, and winning semifinalists will move on to the finals in Boston in July. One player who probably will be plunking down tiles in Beantown--barring an unlikely early-round upset--will be Joel Wapnick, the defending North American Scrabble champion. Wapnick, who gained the crown during tournament play in Chicago in 1983, already has been training intensively.

Just to give new tournament players an idea of what they`ll be facing at the top level this year, Wapnick, a music professor at McGill University in Montreal, has memorized 16,000 seven- and eight-letter words in preparation for his bid to retain the title. He silently runs through his stockpile of words while he shaves and walks his dog. There was a time when he regularly solved newspaper anagram puzzles, but he has found lately that they`re too easy.

During the 1983 tournament, Wapnick played 27 ''bingos.'' A bingo is made when a player uses all seven tiles on his rack to make a word. This is a difficult thing for everyday players to do and earns a player 50 extra points. Wapnick`s highest-scoring word in the 1983 tournament was SLUDGED, a bingo that earned him a total of 98 points.

That particular play also involved a big bluff. In the world of Scrabble, SLUDGED is not a legitimate word. While you can find SLUDGE as a verb--and SLUDGED as its past tense--in Webster`s Third, Scrabble players use the Official Scrabble Players Dictionary as their arbiter of allowable words, and the O.S.P.D. does not contain SLUDGE as a verb.

''SLUDGED was a phony,'' says Wapnick genially. ''I played three phonies in the tournament. When I played SLUDGED, I was down by about 50 or 60 points, so if I had lost that play, I not only would have lost the game, I would have lost it very soundly. But I didn`t think my opponent would challenge the word, and I was right.

''The other two phonies were PUNTIE and HURTLER. HURTLER is close to a real word, which is the trick with a lot of words used as bluffs. PUNTY is a word, but with a Y, not an IE. The plural, though, is PUNTIES, so if you don`t know for sure that the singular ends with Y, it`s hard to challenge the word. ''You have to be very careful when you`re doing this, and you have to know the strength of your opponent. When I played SLUDGED, my opponent on his previous play had played a bingo, the word VIBRANT. But he could have put the letters in a better place, had he known that VIBRANTS was a word allowed by the Scrabble dictionary.

''I noticed that he didn`t know that, so I felt that his word knowledge was not perfect and that I had a pretty good chance of getting away with SLUDGED.''

This is pretty heady stuff for those of us who exult in finding a way to use more than four letters per turn. It is a little humbling to hear Wapnick relate good-naturedly that his highest-scoring game during the tournament was ''513 or 520, something like that'' and that he played ''a bunch of bingos'' during that game, including ZOOLATER (a worshiper of animals). But then, Scrabble is something more than a pastime for him.

''For the last tournament, I memorized in sequence 11,000 seven- and eight-letter words,'' says Wapnick. ''For this one, I`ll have 16,000 memorized. It`s about like memorizing a 70-page book of nonsense words.

''I`ve already memorized these words at least once. Right now, I`m dredging them up because I`ve let them lie dormant in my memory for a long time. I`m getting back anywhere from 200 to 400 a day. In another month or so, I should be back to full strength. Then I`ll just have to rehearse them constantly until July.

''I used to do the JUMBLE anagram puzzle that runs in the paper. The one that appears on Sunday usually has six anagrams, and all are six letters. I can do all six anagrams in about 10 seconds now. It`s not a gift. It`s a matter of practice. When I started, I sometimes would spend a couple minutes on just one of them and sometimes not be able to get it.

''I do rehearse words when I`m walking the dog or shaving. I get good use out of my so-called wasted time. I know a guy in Montreal who has made cassettes of words, and he puts them on his auto tape player and plays them back.''

Clearly, training is taken seriously in the big leagues of the scrambled- word game. What, you wonder, is the atmosphere like when players of this sort meet head-to-head in a national tournament?

''Basically, it`s good-natured between the games,'' says Wapnick. ''But during a game everything is very serious, and that`s the way it should be. This is a serious competition. For us, it`s our Super Bowl. Fortunately, we don`t have any John McEnroes playing Scrabble. Such a person would probably get thrown out of the tournament. You can`t have people interrupting you and distracting you while you`re playing.''

Following his title win, Wapnick appeared on the ''Today'' and ''Canada A.M.'' TV shows, among others, but the notoriety, he says, ''died down very quickly.'' He has written a book, ''A Champion`s Guide to Winning at Scrabble,'' that might be published this summer, depending on negotiations with Selchow & Righter, manufacturer of Scrabble games.

Would he care to reveal any of the book`s tips for players?

''The only thing I can say is try to have a good idea of who you`re playing,'' advises Wapnick. ''If you`re playing somebody who is experienced in tournaments, the one thing you should not try to do is play a word you don`t think is in the dictionary. Don`t try to bluff a good player.''