“The search program serves a special need and, on balance, is reasonable.” That’s the verdict of three federal appeals court judges who have now joined a federal district court judge in granting a constitutional imprimatur to Commissioner Kelly’s program of random bag searches on the city’s subway.The New York Civil Liberties Union had challenged the searches on the grounds that they violated the Fourth Amendment’s prohibition on unreasonable searches and seizures, even though, as reported on this page in November, the front desk at the building in which NYCLU rents its headquarters office conducts such searches of visitors. The federal judges swatted away that constitutional argument in a ruling that contains two important elements.

The ruling is a shot across the bow at so-called civil libertarians who have bemoaned the supposed loss of personal freedom they claim has accompanied the war on terror. As the ruling by the judges riding the Second Circuit points out, the courts have long recognized that the Fourth Amendment isn’t an absolute ban on warrantless searches. Rather, the standard is whether such a search is “unreasonable,” a word that the Founders placed inside the actual text of the Constitution to make it clear that reasonable searches are allowed. And one of the beautiful things about this approach is that it doesn’t have to be changed by circumstance; September 11 has not required the government or the courts to re-define “unreasonable.”

Decades of precedent have established that law enforcement can engage in limited warrantless searches in a variety of contexts, from airport screenings to highway sobriety checks to border patrol stops. Such searches are perfectly constitutional as long as, among other elements, they satisfy a “special need” apart from ordinary evidence-gathering for purposes of prosecution, and there’s a weighty and immediate “government interest,” meaning there are substantial reasons to fear a particular threat that can be addressed through the search.

The subway searches, the judges concluded, fit neatly within the constitutional framework that pre-dates September 11. It’s a refreshing finding as each new police tactic in the war on terror seems to bring yet another onslaught of hollering from the civil liberties crowd. Counter-terrorism certainly is exposing the public to new police tactics, but that doesn’t mean those tactics are unconstitutional. More to the point, the enemy is using new tactics to come at us, a point to which the Civil Liberties Union seems impervious.

The NYCLU had also asked the courts to find that the police department’s bag searches weren’t the most effective method the department could use. Friday’s ruling stands out because the judges pointedly refused to consider that issue. In a display of judicial restraint, the panel, comprising judges appointed by Presidents Nixon, Carter, and Clinton, wrote, “Counter-terrorism experts and politically accountable officials have undertaken the delicate and esoteric task of deciding how best to marshal their available resources in light of the conditions prevailing on any given day. We will not — and may not — second-guess the minutiae of their considered decisions.” That emphasis is in the original. This is a point the courts have too often missed, most recently in the Supreme Court’s Hamdan ruling.

The war on terror has elicited a record number of citations of Benjamin Franklin’s pronouncement that “those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.” The riders of the Second Circuit comprehend that this has often been a false choice. Measures like the bag search program can purchase great safety for the public at the cost of absolutely no traditional liberty.Which leaves New Yorkers free to thank Commissioner Kelly and the officers of the police department for finding yet another constitutional method to protect the city from terrorist threats.