The attack had echoes of the harsh tactics used during the province’s most violent years by the I.R.A., which made a policy of killing not only soldiers and policemen but also civilians whose work supported them. That violence, and attacks by Protestant paramilitaries, killed as many as 300 people a year at the height of the sectarian struggle, but the advent of power sharing has made political killings a relative rarity. Last year, only three deaths were attributed to sectarian attacks.

But fears had grown recently that attacks by dissident republicans were mounting. The dissidents wounded several police officers in 15 attacks in the past 17 months, and a 250-pound bomb was defused last month outside another army base. Sir Hugh Orde, the province’s police chief, announced last week that concern about the attacks had caused him to ask for help from a “small number” of troops from the army’s Special Reconnaissance Regiment, an intelligence-gathering unit based on the British mainland.

That decision ran counter to the reduction of army units under the peace accord, which has cut the pre-1998 British garrison from a high of 25,000 troops to barely 4,000, concentrated on 10 bases that no longer play active roles in the province’s security.

The men killed Saturday were from an engineering unit only hours away from deployment to Afghanistan. The British military identified them on Monday as Mark Quinsey, 23, and Patrick Azimkar, 21.

On Sunday, as the police announced that they had recovered the Antrim gunmen’s getaway vehicle at Randalstown, about five miles west of Antrim, Protestant leaders said the attack had vindicated the police’s decision to call on the army intelligence specialists. The move was condemned last week by Martin McGuinness, the former I.R.A. commander who is the province’s deputy first minister, as “stupid and dangerous” for reviving memories of the role played by army intelligence units in strikes against the I.R.A. in the past.

Image A man left flowers near the Massereene army base, northwest of Belfast, where two British soldiers were shot and killed on Saturday night. Credit... Peter Morrison/Associated Press

But that disagreement was stilled as leaders on both sides of the historic divide joined in condemning the attack, showing a common front that many in Northern Ireland saw as a measure of how far the province had come under the power-sharing accord. Mr. McGuinness and Peter Robinson, the province’s first minister and head of the Democratic Unionist Party, the most powerful of the mainly Protestant parties in the province, announced they were postponing a joint investment-promoting trip to the United States that was to have begun on Sunday.