Probably the biggest event this week is not musical but traditional. Monday is Halloween, the day for goblins, ghosts, Charlie Brown in the pumpkin patch, and Bobby "Boris" Pickett and the Krypt-Kickers Five.

And who is Bobby "Boris" Pickett? He is probably the best-known performer of Halloween music in pop history. Granted there is not a large Halloween pop music catalog, but Pickett's "Monster Mash" is taken out of mothballs every year about this time and spun on radio-station turntables throughout the country. Then, when the last witch has flown her broom into the dawn of November, Pickett is retired to the "special occasion" bins until the next year.

"Monster Mash" is an example of holiday music, a genre never really thought about until said holiday approaches - largely because only one holiday has any great quantity of its own music, and Christmas, as the song says, comes but once a year.

Still, Halloween has its share of one-shots and, far more than Christmas, offers a challenge to willing radio program directors who attempt to sneak Halloween spirits into top-40 or album-oriented rock formats.

In the one-shot category, besides the afore mentioned "Monster Mash" (which may be the "White Christmas" of Halloween tunes), two that spring immediately to mind are Sheb Wooley's "One-Eyed, One-Horned, Flying Purple People-Eater" and "Haunted House" by "Jumpin'" Gene Simmons. Strangely enough, both were hits without the help of jack-o-lantern promotion, "One Eyed . . . " in 1958 a Both dated badly but resurface around now for a brief moment in the spooky spotlight.

Some of the rock songs heard mroe now than any other time include the Eagles' "Witchy Woman," Bruce Springsteen's "Spirit in the Night" (now there is also Manfred Mann's version, which should allow Bruce a brief rest), the Flying Burrito Brothers' "Devil in Disguise" and Edgar Winter's "Frankenstein."

Luckily for everyone, Halloween's menace takes many forms. Thus, we get new implications from the Byrds' "Mr. Spaceman," Norman Greenbaum's "Spirit in the Sky," the Jefferson Starship's query "Have You Seen the Saucers?" and Elton John's reply "I've Seen the Saucers," The theme from "Star Wars" should also continue to be a late-autumn biggie.

There are also the specials. Many people will tune in Orson Welles' "War of the Worlds" (Welles' voice seems to be automatically associated with anything eerie) and some may find the Alan Parsons Project's first album, "Tales of Mystery and Imagination," a Halloween hit. Since "Tales . . . " is essentially Edgar Allan Poe put to music, this is a ghoulish literary event that passes for rock'n'roll.

Halloween has never made anyone's vocal career the way Christmas made Bing Crosby's and Nat King Cole's (unless you count one record a career). Yet, Bobby Pickett returns annually and, sandwiched between, say, Fleetwood Mac and the Steve Miller Band, he should again add a comically reassuring touch to an already mock-serious musical subset.