ST. LOUIS (AP) _ Admirers of Richard Serra's giant downtown sculpture, a triangular composition of seven rusting slabs of steel, say it's on the ''cutting edge'' of art. But a city politician and others say it is a piece of ''junk'' that ought to be carted away.

And that's precisely what Alderman Timothy Dee is trying to do with ''Twain,'' the sculpture Serra made at public expense for $250,000. Dee has introduced a bill calling for a public vote on whether the work should be taken down.

''If it was in someone's back yard, no one would care,'' Dee said. ''But people see all these great things going on downtown and they wonder, 'Why is this thing right in the middle of it all?'''

The sculpture's detractors have been encouraged by a similar effort by some New Yorkers to dismantle their own Serra sculpture, ''Tilted Arc,'' another rusty steel wall the government paid $181,000 to erect in front of a federal building. A panel has been formed to find a new location for the sculpture.

Each steel slab of ''Twain'' is between 40 and 50 feet long and stands 6 to 9 feet high. They are less dramatic in appearance than other sculptures in the multi-million-dollar Gateway Mall, an expanse of buildings and parks that begins on the bank of the Mississippi River with the 630-foot-high stainless steel Gateway Arch.

''I like it because it's on the cutting edge of a new awareness,'' said Dr. Beej Nierengarten-Smith, director of the Laumeier Sculpture Park in St. Louis County. ''Over time, people will come to terms with it. They won't necessarily love it. But no one says you have to like it.''

But Dee has introduced a bill in the Board of Aldermen to give city voters the final say on whether the sculpture should be dismantled.

''I certainly have gotten a lot of comments from people in my district before I introduced the bill and since then,'' he said. ''Most say it's a piece of junk and shouldn't be there.''

The earliest Dee's referendum could come to a public vote would be August, but the alderman is confident that voters will ultimately decide to remove ''Twain.''

Michael Shapiro, curator of the Saint Louis Art Museum, wants to give Serra's sculpture ''the benefit of time.''

Supporters of the sculpture installed in 1982 suggest that its detractors haven't tried to deal with ''Twain'' on its own terms. One must become involved with the piece, they say, walk inside it through two-foot-wide openings in the metal slabs and look outside at the city scenes.

Dee said he did just that before he made up his mind to introduce the bill.

''Frankly, it didn't do a lot for me,'' he said. ''It gave me a sense of intimidation rather than an uplifting, creative experience. I felt walled in, sort of trapped. I wanted to make sure I had a good escape route.''

Efforts to reach Serra through his attorney were unsuccessful.

Nierengarten-Smith remains optimistic that ''Twain'' will not be removed.

''The piece needs this controversy,'' she said. ''A lot of people in St. Louis are talking about ''Twain'' who never gave it much notice before.''

''I've never heard a piece of sculpture scream: 'Touch me warmly and love me dearly,''' she said. ''But we don't resolve the issue by wiping it out.''