A federal judge cleared the way Tuesday for the city of San Francisco to ban most displays of public nudity, ruling that an ordinance set to take effect on Feb. 1 does not violate the free speech rights of residents and visitors who like going out in the buff.

U.S. District Court Judge Edward Chen refused to block the ban temporarily or to allow a lawsuit challenging it to proceed.

"In spite of what plaintiffs argue, nudity in and of itself is not inherently expressive," Chen wrote in an 18-page opinion.

The San Francisco Board of Supervisors voted 7-4 last month to prohibit residents and visitors over age 5 from exposing their genitals on public streets, in parks or plazas or while using public transit.

The measure was introduced in response to a group of nudists that regularly gathers in the city's predominantly gay Castro District. The threat of seeing outlawed a right that many people associate with free-spirited San Francisco prompted public protests and disrobing at supervisors meetings.

The activists who challenged the measure in court also had argued that the ordinance was unfair because it grants exceptions for public nudity at permitted public events such as the city's gay pride parade and the annual Bay-to-Breakers foot race.