British Prime Minister Tony Blair was hardly exaggerating when he hailed yesterday's stunning renunciation of violence by the Irish Republican Army as "a step of unparalleled magnitude." That it most certainly can be.

But will it be?

On the surface, the announcement seems unambiguous: "The leadership has formally ordered an end to the armed campaign," announced the IRA. "All volunteers have been instructed to assist the development of purely political and democratic programs through exclusively peaceful means. Volunteers must not engage in any other activities whatsoever."

And its implementation was said to be immediate: All IRA units were ordered to disarm; former Canadian Gen. John de Chastelain was invited to witness the destruction of weapons stocks.

Caution is called for; all of this was meant to have taken place, under the Good Friday accord, five years ago.

Which is why Irish Prime Minister Bertie Ahern stressed that it will only prove historic "if the IRA's words are borne out by verified actions."

But this announcement seems to have the ring of sincerity behind it.

And, if it is for real, it represents a singular victory in the global War on Terror — thanks primarily to the determination of Tony Blair and Bertie Ahern, who refused to compromise on the issue of stripping the IRA of its weapons.

President Bush did his part, too: Following some recent IRA outrages, its "political" wing, Sinn Fein, found itself barred from the White House for the first time in more than a decade.

Just as important, such longtime U.S. allies of the IRA as Rep. Peter King denounced it and called on it to disband.

No doubt, this growing political isolation helped the IRA see the light.

All of which underscores how far the IRA has moved from its original revolutionary purposes. It maintained close ties with the global terrorist cartel, receiving 130 tons of arms from Moammar Khadafy in the '80s, hosting the PLO at its annual meetings and training Marxist terrorists in Colombia.

And, like opposing Unionist paramilitaries, it has been heavily involved in the Irish rackets. Even since the signing of the Good Friday agreement, the IRA has resisted calls for it to renounce crime and violence and dragged its heels on disarmament and accepting a power-sharing government in Northern Ireland between Catholics and Protestants.

So a note of skepticism is called for.

The IRA will have to prove that it has accomplished in deeds what it yesterday promised in words. And Unionist obstructionism will doubtless remain a real threat to peace.

But real optimism is appropriate.

Thanks to the determination of those leaders who refuse to compromise in the War on Terror, there now is hope, as Prime Minister Blair noted, that "this may be the day, after all the false dawns and dashed hope, when peace replaced war [and] politics replaces terror on the island of Ireland."