"This is a step of unparalleled magnitude in the recent history of Northern Ireland," he said.

The statement by the IRA said that its leadership had "formally ordered an end to the armed campaign," as the organization calls its military activities, which are described by supporters as armed struggle and by adversaries as terrorism.

The shift followed growing revulsion among its Catholic supporters, both here and in the United States, at the I.R.A.'s involvement in organized crime and, since Sept. 11, at global terrorism.

"Our decisions have been taken to advance our republican and democratic objectives, including our goal of a united Ireland. We believe there is now an alternative way to achieve this and to end British rule in our country," the statement said, apparently referring to the advances of its Sinn Fein political arm in both Northern Ireland and the Irish Republic.

"All I.R.A. units have been ordered to dump arms," said the statement, which was read on the DVD by a former I.R.A. prisoner, Seanna Walsh. The statement also pledged "to complete the process to verifiably put its arms beyond use" - a reference to the I.R.A.'s reputedly vast hidden stockpiles of weapons. The I.R.A. also invited two independent clerics, one Catholic, one Protestant, to "testify" to disarmament.

The statement did not say the I.R.A. was disbanding and did not refer specifically to the issue of crime by I.R.A. members, held responsible for a huge bank heist last December and a brutal barroom murder and cover-up in January.