WHEN an anti-Islamic group decided to advertise on city buses and billboards this fall with photos of a terrorist poised to behead an American and a Muslim leader smiling at Adolf Hitler, transit officials in New York and Washington, D.C., huffed their disapproval - but allowed the ads to run.

They had no choice, they said, because the ads were protected under the First Amendment.

SEPTA's officials disagreed and rejected the ads.

But the group behind the ads - the American Freedom Defense Initiative - won't surrender quietly. The New Hampshire-based group sued SEPTA in federal court last week, complaining that the transit agency violated AFDI's free-speech rights.

One local First Amendment expert says SEPTA picked an unwinnable fight.

"The most fundamental principle of the First Amendment is that you may never bar any message based upon the content of the message," said Burton Caine, a law professor at Temple University and past president of the Philadelphia chapter of the American Civil Liberties Union. "This is absolutely prohibited, what SEPTA is doing.

"Everybody has this same idea that they like the First Amendment," Caine said, "but when the speech is offensive, people will make all kinds of excuses why it's not protected. The whole point of the First Amendment is to protect speech that offends. No exceptions."

A federal judge said as much in 2012, ruling that the AFDI could post ads in New York City and Washington, D.C., that compared Muslim jihadists to "savages."

The AFDI ad that SEPTA rejected in June showed Haj Amin al-Husseini, a pro-Nazi Palestinian leader in the 1930s, smiling at Adolf Hitler beside the caption "Islamic Jew-hatred: It's in the Quran. Two thirds of all US aid goes to Islamic countries. Stop the hate. End all aid to Islamic countries."

SEPTA spokeswoman Heather Redfern said she could not comment on pending litigation.

AFDI has been identified as a hate group by the Southern Poverty Law Center. AFDI's president, Pamela Geller, is a far-right blogger who also founded the group Stop Islamization of America.

On Twitter: @DanaDiFilippo

Blog: phillyconfidential.com