Blood may be replacing sex at the movies. The number of films that are excuses to watch people copulate seems to have leveled off, so to speak, but there's a boom on movies that are excuses to watch people bleed to death.

The newest, and one of the most pretentious, is "Martin," a film by George Romero, whose "Night of the Living Dead" in 1970 attained the high distinction, in the genre, of being called "a cult movie."

"Martin" is pretentious in a way that pornography is when it is dressed up for people who don't want to admit to their taste. We're not really coming for that , it seems to say; that is just there because it is an integral part of the story.

Sure it is.

"Martin" is a film about a punk who goes around killing people in the messiest possible way. Blood in all over the screen most of the time. But no fewer than four different excuses have been supplied, to disguise the fact that it's designed for people who like bleeding.

Excuse 1: This is really a literary movie, the concept of the Vampire being a mythology that explains allegorically the human predicament. The film is full of references of Vampire lore, with the repeated assertion that this is adding to a long literary tradition with new information.

Excuse 2: This is really a historical film, showing us our roots. Each scene in the present reminds Martin of something that happened to him in the previous century. However, this is kept to a minimum because of course the past took place in black-and-white, and blood doesn't show up as well as in our colorful present.

Excuse 3: This is really a psychological film, expressing the alienation of modern youth. The Vampire looks like the other rotten kids on the block, and is constantly throwing out clues for the analyst: "It's just that I'm shy . . . "In real life, you can't get people to do what you want them to do."

Excuse 4: This is really a satirical movie, making fun of all those other movies that cater to people who really like horror movies. There are several references to how "It's not really like the way they did it int 'The Exorcist,'" and the Vampire's confidant is the host on a call-in radio show.

Of all the excuses offered No. 4 is probably the lowest. If people want to enjoy pornography, or blood, they shouldn't claim to be doing it out of superior feelings based on putting down people who admit enjoying it.

But then, nobody really enjoys watching others bleed to death - and the people who buy pornographic magazines do it only because they enjoy the articles about the economy that separate in pictures.