"We've come back, so you come back!" proclaim ads for the subway system. And, less than two years after it was pronounced dead, graffiti seems to be coming back, too.

"You're seeing a lot of `Dick Loves Mary' kind of stuff, or a kid on the way home from school writing his `tag' on a wall," Lt. John Romero of the transit police vandalism squad said this week.Subway car graffiti "hits" doubled in 1990 to 46,000, according to Dick Goodlatte, the Transit Authority's chief mechanical officer. Transit police made 372 arrests for graffiti writing in the first 11 months last year, compared with 160 in 1989.

Last week, after a series of major hits forced several cars out of service at rush hour, the TA's anti-graffiti task force met for the first time in 18 months.

"Everyone agreed it's getting worse," Goodlatte said. "But no one was sure why."

If the TA has lost ground since May 12, 1989, when it ceremoniously retired the last graffiti-covered car, it still has come a long way from the days when hundreds of youths regularly spray-painted the system's 6,000 cars, usually while the cars were at train yards.

"Our major hits are not what they used to be," Romero said. He estimated that only two dozen writers still attempt "major pieces."

When graffiti first appeared around 1970, some welcomed it as a vital new art form, and teenage writers with tags such as TAKI 183 became folk heros. There was an appreciative essay by Norman Mailer and a movie, "TURK 182."

The outsides of cars were covered with colorful, flamboyant murals, some requiring dozens of cans of paint and hours of work. Inside, the cars were a jungle of scrawls and scribbles; passengers felt they were riding in a twisted cartoon.

Soon a negative reaction set in. A conspicuous reminder of the subway's decline and the Transit Authority's lack of control, graffiti became what one columnist called "the most famous emblem of the city's madness."

In 1984 the TA began to clean cars as soon as graffiti appeared, even if it meant service delays. The theory: If riders saw less graffiti they'd feel better about the subway, and if the writers saw less of their work, they'd lose interest.

Over the next five years, annual subway graffiti arrests dropped from 2,612 to 160, and the TA declared its fleet graffiti-free.

That declaration proved premature. "You will never eliminate graffiti," Romero said.

Determined writers walk on the tracks into fenced yards and other areas where trains are parked, Goodlatte said. "These people are brazen," he said. "They'll come up in a car next to a cleaner and spray it as he's cleaning it."