The Boy Scouts of America's Philadelphia chapter has sued the City of Philadelphia in federal court to block the city's May 31 deadline for the scouts to open membership to gays and atheists, or vacate their historic 1928 headquarters off Logan Square.

The civil rights lawsuit, filed Friday in federal court in Center City, contends that the city's ultimatum violates the scouts' rights under the U.S. and Pennsylvania Constitutions.

"The City has imposed an unconstitutional condition upon Cradle of Liberty's receipt of a benefit that Cradle of Liberty has enjoyed for nearly eight decades, and that many other organizations that limit members or services to members of a particular group continue to enjoy without punishment or the threat of punishment," the scouts' lawsuit reads.

City Solicitor Shelley R. Smith said the city would respond to the federal lawsuit and would likely file an eviction motion next week.

In the meantime, Smith added, the beginning of litigation would preserve the status quo pending a court ruling. Until that ruling occurs, Smith said, the scouts will be able to continue using the headquarters building.

The suit asks the court to permanently block city officials from attempting to evict the Scouts from their building, which sits on a half-acre of city land at 22d and Winter Streets.

The Cradle of Liberty Council's predicament is one that has faced local scouting councils nationwide since a 2000 U.S. Supreme Court case the scouts won.

The national organization appealed the ruling in a suit filed by an openly gay New Jersey scout barred from serving as a troop leader.

Scouts must swear an oath "to God and my country" and to "obey the Scout Law" that includes keeping oneself "physically strong, mentally awake, and morally straight."

In 2000 the Supreme Court ruled 5-4 in Boy Scouts of America v. Dale that the scouts are a private group and thus have the right of "expressive association" under the First Amendment to set their own membership rules.

The legal victory was short-lived as municipal officials nationwide began reexamining longstanding relationships with local scouts. Unlike the scouts, local public officials were bound by another line of Supreme Court opinions that barred taxpayer support for any private group that discriminates. Other mainstream supporters, such as United Way, also dropped them.

Last October, after several years of sporadic talks between city and council, the city imposed the May 31 deadline: Change your membership rules, vacate the building, or pay a fair market rent of $200,000.

The scouts have maintained that they cannot change their membership policies without being ejected by the national scout organization and cannot afford the rent.