Seth Morgan, who won acclaim last spring for his first novel, ''Homeboy,'' which drew on his experiences in the drug culture of San Francisco and in prison, was killed early Wednesday morning when the motorcycle he was driving struck a dividing post on a bridge in New Orleans, the police said.

Mr. Morgan, who was 41 years old, and a passenger, Diane Levine, 37, both of New Orleans, were thrown from the motorcycle and were pronounced dead at the scene, the police said, adding that neither of them had been wearing helmets as required by state law.

Early Tuesday morning, Mr. Morgan was arrested and charged with driving his motorcycle while intoxicated, they said, but it was not known if he was intoxicated at the time of the accident.

Reviewing ''Homeboy'' in The New York Times Book Review last May, Deborah Mason called it a ''savagely comic and often brilliant'' look at ''the teeming San Francisco nether world of junkies, pimps, drag queens and hookers.'' With sometimes ''hallucinogenic prose'' and ''the picaresque authority of a Joycean Hell's Angel,'' she wrote, Mr. Morgan created ''an unnerving and utterly persuasive rendition of hell.''

Second Novel Was Planned

Jason Epstein, one of Mr. Morgan's editors at Random House, said that ''Homeboy'' had sold 25,000 copies, which he described as a great deal for an unknown writer. He said Random House had signed a contract with Mr. Morgan for a second novel, set in New Orleans and called ''Mambo Mephiste.''

In a two-page autobiography for his publisher, Mr. Morgan recalled growing up in New York City surrounded by ''literary jawboning,'' attending a ''school for monied misfits'' in Switzerland and dropping out of the University of California at Berkeley to move in with Janis Joplin shortly before her death. He worked as a barker for strip-tease clubs in San Francisco before and after his imprisonment in California from 1977 to 1980 for armed robbery. Then, he wrote, ''On my last legs, I hied down to New Orleans to quietly drink myself to death, and nearly did, but something awoke in me and I wrote a book instead.''

He is survived by his father; his stepmother, Paula Dietz; two sisters, Gaylan, of Cambridge, Mass., and Veronica, of Amherst, Mass., and a brother, George, of Point Pleasant, Pa.

Seth David Morgan