Plainclothes sheriff's deputies on Santa Monica Boulevard arrested 18 suspected male prostitutes during an undercover vice operation that ended early Saturday, police said. The undercover deputies, wearing street clothes and driving unmarked cars, drove up and down the boulevard between La Brea Avenue and La Cienega Boulevard between 7 p.m. Friday and 3 a.m. Saturday. Eighteen men were arrested after soliciting the undercover deputies for sexual acts. They were booked at the West Hollywood sheriff's station for disorderly conduct and prostitution. Bail for each was set at $2,500. Deputies said 45 male prostitutes have been arrested in West Hollywood undercover operations since January. Area merchants have been complaining about the prostitution, police said.