The ads in the adult section, which cost $10 to post and $5 to repost, are a big revenue source, analysts say. Craigslist is private and does not report financial figures. But adult ads are expected to bring the company $45 million in revenue this year, according to the Advanced Interactive Media Group, an organization that analyzes Craigslist.

Some Internet law analysts said on Saturday that Craigslist could be sending more than one signal — that it was both capitulating to law enforcement and thumbing its nose at it.

“There are multiple ways in which to censor speech — one is directly through the courts, and the other is through a form of protest that says, even if you can do this, stop doing it,” said Thomas R. Burke, a lawyer at Davis Wright Tremaine who specializes in Internet law and is not involved with Craigslist. “Maybe their point in saying they were censored is that people need to understand the law better.”

But Malika Saada Saar, executive director of the Rebecca Project for Human Rights, a nonprofit group that has urged Craigslist to shut the adult services section and screen the entire site for such ads, said the company should be held responsible for what appears on its site. She said Craigslist “has the legal responsibility as well as the moral responsibility” to close the section. Craigslist has taken steps to appease critics before. In May 2009, it removed its “erotic services” category and replaced it with “adult services,” for “postings by legal adult service providers,” and had all adult services ads manually screened by a lawyer before posting.

But criticism has continued, fueled by prominent cases like that of Philip Markoff, a Boston medical student who was charged with murdering a woman he had met on Craigslist. He pleaded not guilty, and he died in jail last month in an apparent suicide.

The section in question appears not to have been blocked abroad. In France visitors to the site have access to the Érotique link and can see material intended for adults.