LONDON, JAN. 28 -- A 13-year battle to reverse the convictions of six Irish men for Britain's most devastating terrorist attack, the 1974 bombing of two Birmingham pubs that left 21 people dead and 160 injured, failed today when the High Court rejected an appeal of the original verdict and life sentences.

The case long has been politically sensitive, with many British and Irish politicians, as well as international organizations, saying the men were innocent. They have said that the original convictions were based on suspect forensic evidence and that the defendants confessed only after being beaten by police.

In a statement tonight, the Irish government said it had "learned with great regret and disappointment" of the decision, which it said "has not removed the serious concern which has been consistently expressed by the government and conveyed to the British authorities, that there may have been a miscarriage of justice in these cases."

In London, opposition Labor Party Member of Parliament Chris Mullin, who led the campaign on behalf of the men and claims to have spoken to the actual guilty parties, called it a "black day for British justice."

The decision against the so-called Birmingham Six is the second major blow in four days to Anglo-Irish relations. Some political leaders said they feared events this week may have done irreparable harm to the landmark agreement signed by the two governments in November 1986 in which they established a joint commission to help ease tension in troubled Northern Ireland.

Former Irish foreign minister Peter Barry, one of the main architects of the agreement, said there had been "enormous resentment" in Ireland over the case.

On Monday, Britain said it would not prosecute Northern Irish police officers involved in a separate inquiry into an alleged "shoot to kill" policy reportedly followed in the province in 1982.

Following Monday's announcement, Ireland called for an emergency meeting of the Anglo-Irish commission. Prime Minister Charles Haughey said today that although he recognized the difficulties faced by security forces in Northern Ireland, "perjury, misleading statements to the authorities and other actions designed to pervert the course of justice should not be tolerated."

In an apparent attempt to dampen Irish anger over the decision against further prosecutions in the "shoot-to-kill" matter, British Northern Ireland Secretary Tom King said today that internal disciplinary action against the police officers involved was still under "urgent" consideration.

Beginning in 1985, new questions were raised about forensic testing and alleged police mistreatment of the six in the days following their arrest and an appeal hearing was granted a year ago.

The three-judge appeals panel today dismissed the alleged new evidence as insubstantial, and the witnesses as unreliable.