IF Gerry Adams decides to march up Fifth Avenue in the St. Patrick's Day parade this weekend, New Yorkers will see a politician whose dented credibility can be rescued by only one thing.
The leader of the political arm of the Irish Republican Army - Sinn Fein - desperately needs the IRA to restore the cease-fire it shattered with a bomb in London on Feb. 9.
Anything less, governments in London, Dublin, and Washington are telling Mr. Adams, will leave him out in the political cold. For Adams, such abrupt exclusion from the corridors of power represents his worst setback in a 25-year political career.
A few weeks ago he was shaking the hand of President Clinton and was seen by many Irish-Americans as a peace-seeking hero. But as he left Belfast for the US on March 12, he said his latest American journey would ''have its limitations.''
The first priority, he said, was ''to get the peace process back on the rails as quickly as possible.''
British government ministers say that may be impossible for the man who was born in Catholic Ballymurphy and was out protesting in the streets of Londonderry in 1969 when a new round of Northern Ireland's ''Troubles'' began to erupt.
Later, through what opponents concede are force of character and intellect, Adams rose to head the province's republican movement in which he has said he started ''as a foot soldier.'' Despite his insistence that he is still the authentic leader of that movement, British Premier John Major challenges that claim.
''Until he can persuade the IRA to give up violence,'' Mr. Major said after the Feb. 9 bombing, ''we must question his authority.''
Over the years, successive British governments have expressed serious hesitations about Adams's relationship with the IRA. Before he became president of Sinn Fein in 1986, British security officials identified him as either an active IRA member or a person intimately involved in its strategy of terrorism.
''The distinction between Sinn Fein and the IRA is a fiction,'' says a senior Conservative parliamentarian. ''The truth is that Adams at the moment belongs to a wing of the IRA that has lost control to more ruthless men and women. He may be a politician these days, but he was a guerrilla in earlier years.''
But Adams says that until he saw Northern Ireland Protestants looting and burning Catholic homes in the 1960s, he had no interest in politics. ''I was drawn into the struggle by that experience,'' he says.
EVEN now the precise role of the tall, bearded, bespectacled intellectual who claims to be a peacemaker is a mystery, says author James Dalrymple. ''To loyalists, who despise and fear him, and to the British media which demonizes him, he is a former gunman and bomber who has adopted the mantle of pacifier,'' he says. But to Catholics in West Belfast he is ''truly one of theirs - a leader in the patriot game.''
Today, Adams's battle to recover credibility in Northern Ireland and worldwide leads him into apparent contradictions.
A week ago, he warned Britain that the IRA was prepared for ''another 25 years of war.'' It sounded like a threat. But on Wednesday in New York he appealed for calm ''in a very dangerous situation.''
Such apparent ambivalence, says political analyst Brendan O'Leary, will undermine Adams's claim to be a man of peace so long as the IRA's campaign of violence continues.