WASHINGTON — With the Irish-American vote at stake in November, the Obama campaign is lashing out at Senator McCain over his opposition a decade ago to allowing into America a Northern Ireland leader linked to terrorism.

A group of senior Democrats yesterday accused the Republican presidential nominee of standing on the wrong side of a move that many Irish Americans see as critical to the peace accord signed in 1998 between the British and Irish governments: President Clinton’s decision to grant a visa to Gerry Adams, the leader of Sinn Fein, the political arm of the Irish Republican Army. The State Department had labeled the IRA a terrorist organization before the 1998 agreement, and the group did not renounce an armed campaign against Britain until 2005.

Mr. McCain ridiculed Mr. Clinton at the time, saying he had undermined American credibility and “damaged” the nation’s relationship with Britain. In an article in the journal Foreign Policy in 1996, Mr. McCain wrote that the push to allow Mr. Adams into America was “motivated by romantic, anachronistic notions of Irish republicanism.”

The Obama campaign dredged up his comments yesterday, looking to drive a wedge between the Arizona senator and the Irish-American community, which could play a key role in battleground states such as Pennsylvania and Ohio.

“He seemed to have absolutely no understanding of the history involved or how important it was to bring both sides of that conflict together,” Senator Leahy, a Democrat of Vermont, said of Mr. McCain during a conference call yesterday.

The Obama campaign’s attack of Mr. McCain’s decade-old position on the Adams visa underscores how aggressively each campaign is courting Irish voters heading into the campaign’s home stretch.

But its decision to embrace a figure so closely tied to a terrorist group could be risky at a time when the Republicans are increasing their efforts to link Mr. Obama to William Ayers, a former member of a radical Vietnam War-era group that bombed American government buildings in the 1970s.

Mr. Obama’s surrogates characterized Mr. Clinton’s decision on Mr. Adams as a controversial move that has been vindicated by history, and they are buffeted to some extent by the fact that even Mr. McCain has praised the former president’s involvement in the Northern Ireland accords, even as he has stayed mum on Mr. Adams.

“That moment may not seem like much to people, but it was pivotal,” Senator Dodd said of the Adams decision. “At the key moment, when an American president decided to do something no one else had done, and take that chance and grant Gerry Adams a visa, it opened the door from which all else followed.”

Democrats active in the Irish-American community acknowledge that Mr. Obama’s struggle to win over working-class voters and Mr. McCain’s moderate stance on immigration give the Republican a unique opportunity to win over Irish voters.

“It’s very much more up for grabs now,” a former Democratic New York state assemblyman who now serves as chairman of the Irish American Presidential Forum, John Dearie, said of the Irish vote.

Mr. McCain became the first Republican presidential candidate to participate in the forum, established in 1984, which he held in the form of a town hall meeting yesterday in Scranton, Pa.

He pledged his support for comprehensive immigration reform, and he promised to appoint a special envoy for Northern Ireland, a practice begun by Mr. Clinton in the 1990s that Irish-American activists view as an important commitment from the presidential candidates. Mr. McCain also said in prepared remarks that he would “welcome peacemakers to the White House,” although he did not mention Mr. Adams.

The Democrats said Mr. McCain was merely pandering, pointing to his backing away from the immigration bill he supported after it failed in the Senate amid opposition from conservatives. “He’ll say what he has to say in order to appease the audience he’s in front of right now,” Rep. Joseph Crowley of New York said.

Governor O’Malley of Maryland said of Mr. McCain: “We see the Straight Talk Express now becoming the Blarney Bus.”

A McCain supporter, Rep. Peter King of New York, said the Arizona senator was late in joining the American push for a resolution to the conflict in Northern Ireland but that he has since “climbed on board.”

“He is very supportive of the Irish peace process,” he said. Mr. King, who was a vocal advocate of granting Mr. Adams a visa, also suggested that Mr. McCain would likely regret his opposition to the move. “He would probably say the Clinton decision turned out to be right,” he said.

A spokesman for the McCain campaign, Tucker Bounds, declined to say whether Mr. McCain stood by his opposition to the Adams visa. “John McCain enjoys incredible support from the Irish-American community, and his strong record of fighting on issues important to Irish-Americans has solidified his base of support,” he said.

Mr. McCain instead picked up on a vulnerability of Mr. Obama’s, pointing out a statement last month from the Democratic campaign that questioned whether a special envoy remained necessary.

The suggestion angered many in the Irish community, and the Obama campaign quickly walked it back. His surrogates yesterday insisted that Mr. Obama was committed to keeping the post.

“That question has been squarely answered,” Mr. Crowley said. He suggested the revised stance was a result of Mr. Obama seeking advice from lawmakers who were more experienced in Irish-American diplomacy. “It also demonstrates that Senator Obama is looking to people who maybe have a greater understanding of these issues than maybe he does,” he said.