The region’s top federal law enforcement official has filed a lawsuit aimed at blocking Philadelphia from becoming home to the nation’s first supervised drug injection site, even as backers of the idea continue to move forward with their plans.

The suit, filed by U.S. Attorney William M. McSwain late Tuesday and made public Wednesday, asks a judge to declare such a facility illegal under federal law. McSwain said that by seeking a ruling before any site opened, he hoped he could deter supporters and avoid more drastic steps such as arrests, prosecutions, or forfeiture proceedings.

“It is the [Justice] Department’s job to promote and enforce the rule of law, not to look the other way,” the prosecutor said at a news conference Wednesday at his Center City office. “Normalizing the use of deadly drugs like heroin and fentanyl is not the answer to solving the opioid epidemic.”

Lawyers for Safehouse, the Philadelphia supervised injection site nonprofit, have signaled they have no intention of backing down and believe the law is on their side. Far from normalizing drug use, advocates say, the sites help keep people alive and able to pursue treatment.

The gap between the two positions sets the stage for a first-of-its-kind court battle that could end up shaping legal debate over such sites across the United States.

“We’re certainly glad to see that the U.S. Attorney’s Office is proceeding on a civil track as opposed to a criminal track,” said Ilana Eisenstein, a partner at the international law firm DLA Piper, which is providing free representation for Safehouse. “From our perspective at DLA, we are in it for the long haul to defend Safehouse and to advocate for its legal rights to be able to go forward in its lifesaving mission.”

A handful of other cities, including New York and Seattle, have also inched toward making supervised injection sites a reality as each struggles to combat a drug crisis that has led to thousands of deaths and resisted traditional prevention measures. But with the incorporation of Safehouse, Philadelphia is arguably closest to opening a site.

The magnitude of the crisis here — where an estimated 1,100 people died last year, fueling the worst overdose death rate of any major U.S. city — has prompted some city leaders to warm to the idea, citing potential public health benefits. More than a year ago, Philadelphia’s mayor and district attorney announced they would not stand in the way of allowing a supervised injection site to open, provided it was built and operated with private dollars.

(Asked after an unrelated news conference about the lawsuit Wednesday, Philadelphia District Attorney Larry Krasner said: "The United States population does not think the drug war worked, but [former Attorney General] Jeff Sessions does, I guess [Deputy Attorney General Rod] Rosenstein does, and it would appear Donald Trump and Bill McSwain do, too.”)

Despite opposition from law enforcement officials including McSwain and Pennsylvania Attorney General Josh Shapiro, a coalition of local advocates, including former Gov. Ed Rendell, has committed to moving forward. Within the last year, the supporters have incorporated the nonprofit, hired an executive director, and launched a fund-raising effort for the $1.8 million they project they will need to operate the facility in its first year.

No site has been finalized, but the most likely location is Kensington, the neighborhood that has become both the center and public symbol of the city’s opioid epidemic.

The lawsuit, assigned to U.S. District Judge Gerald A. McHugh, names both Safehouse and its director, Jen Bowles, as defendants. It stops short of asking for an injunction — a ruling that would specifically prohibit the nonprofit from operating in Philadelphia and carry with it the weight of potential sanctions or possible prison time for those who defied it.

Instead, it asks the judge to interpret federal drug laws and draw a conclusion on the legality of supervised injection sites in general.

“We want to take an incremental, reasonable approach,” McSwain said in an interview before Wednesday’s announcement. “We’re not interested in some sort of criminal confrontation or drama or trying to be heavy-handed. We think it serves everyone’s interests for the federal court to issue a declaration as to whether this proposed site is illegal or not.”

Still, his remarks at the news conference at times struck an adversarial tone. “If you think that you’re above the law, you’ll soon find yourself in court to account for your actions,” he said at one point.

Safehouse vice president Ronda Goldfein said she welcomed the opportunity to debate the issue before a judge.

“We are going to present research that supports the notion that supervised consumption saves lives,” said Goldfein, who is also the executive director of the AIDS Law Project of Pennsylvania (and is married to an Inquirer editor, David Lee Preston). “I think that the value of having a court decide this is that it gives both sides the opportunity to present the credible evidence and research that has informed their analysis.”

McSwain’s lawsuit cites a 1986 federal law — known colloquially as the “crack-house statute” — that makes it a felony punishable by up to 20 years in prison to knowingly open or maintain any place for the purpose of manufacturing, distributing, or using controlled substances.

Proponents of supervised injection sites argue that the measure, enacted during the crack cocaine epidemic, was never intended to interfere with good-faith efforts to improve public health.

McSwain maintains that the law is clear and that if projects like Safehouse are to move forward legally, its backers should first lobby legislators to change it.

At his news conference, he touted efforts by his office to respond to the opioid crisis, including its participation in the federal judiciary’s Relapse Prevention Court and through criminal prosecutions, like the charges filed Wednesday against nine doctors and other medical personnel accused of running pill mills in Philadelphia and its suburbs.

He also questioned research that Safehouse’s backers say proves supervised injection sites save lives and get more people into treatment — a potential preview of arguments his attorneys may make in court.

"Safehouse claims that an injection site in Philadelphia would save lives,” he said. “But are we sure about that?”

Reading from a 2017 study the city commissioned on supervised injection sites, McSwain noted that report is focused on North America’s longest-running site, in Vancouver. He also pointed out that the city’s own researchers had noted it was “uncertain” about how relevant the Vancouver statistics could be for other communities.

Because there are no such sites in the U.S., researchers have relied on data from Canada and Europe.

The study commissioned by Philadelphia officials said that within three years of opening its site in 2003, Vancouver saw a 9 percent drop in deaths citywide and a 35 percent drop within 500 meters of the facility.

According to the coroner’s service of British Columbia, overdose death rates rose only slightly or even dropped in the province during the decade after the site opened. It was not until 2013, with the advent of the modern opioid crisis and the fentanyl-laced heroin that followed, that deaths began to rise precipitously.

McSwain correlated the rise in deaths with the existence of the site, telling reporters, “You look at the raw numbers, you open up an injection site in Vancouver, deaths go up.”

As he was speaking Wednesday, a small group of protesters gathered in the lobby of McSwain’s Chestnut Street building, toting a banner that said: “Dead People Can’t Recover."

“This is a public health emergency, and this is one of the responses that needs to happen,” said David Tomlinson, a harm-reduction advocate who helped organize the demonstration Wednesday. “It’s not the solution, but it’s a solution. And the longer they block it, the more people are going to die.”

Goldfein said Safehouse is not in a position to open a site right away. Still, she said: “We have consistently maintained that it’s a legal activity, so we are not necessarily waiting for the lawsuit to be resolved. We’re waiting for other considerations to be in place, like locating appropriate siting and finding funding.”

McSwain said that should they move forward before McHugh, the judge, has ruled, his office would consider seeking an injunction to stop them.

As of late Wednesday the judge had not set a date for a hearing on the suit.