ABINGTON, Mass. (AP) _ An Irishman accused of plotting an armored truck heist is the highest- ranking Irish Republican Army member ever arrested in the United States, a newspaper reported.

Michael Oliver McNaught, 45, an Irish national, was arrested with five other people outside The New Bank of New England on Wednesday. Authorities said the six were awaiting the arrival of an armored truck containing nearly $1 million.

Police said they seized gasoline bombs, handguns, two-way radios, masks and three Uzi machine guns.

Authorities said they were trying to determine whether whether McNaught was connected to the IRA, but the Boston Herald reported Friday that sources revealed he was the highest-level IRA operative arrested in this country.

''We are making inquiries to verify who he is and develop background information,'' said FBI spokesman Bill McMullin. ''We can't say we are investigating his involvement in the IRA simply because we don't know if he was involved.''

Ann Kanter, a spokeswoman for the British Consulate in Boston, said the names of those arrested were passed on to British authorities.

Martin Galvin, a spokesman for the New York-based Irish Northern Aid Committee, dismissed the alleged connection as ridiculous.

''It would be totally absurd for anyone to suggest these men had a strong linkage with the Irish Republican movement,'' he said. ''The movement has not engaged in that type of activity and never would.''

The mainly Roman Catholic IRA is fighting British rule in Protestant- dominated Northern Ireland.

Bill McMullin of the Boston FBI office said McNaught and the other five were arrested by officers who followed a stolen car they had driven to the bank.

FBI officials said the six had been under surveillance since July and have been connected to robberies in Rockland and Fitchburg. The others arrested were: Michael Habicht, 33, of Boston; Patrick Joseph Nee, 46, of South Boston; James F. Melvin, 48, of South Weymouth; Robert Emmett Joyce, 37, of Quincy; and James Michael Murphy, 48. Residences for Murphy and McNaught were not immediately available.

Nee, who pleaded guilty to trying to ship arms to Northern Ireland in 1984, was sentenced to four years in prison in 1987 and freed in 1989.

The six were being held pending a detention hearing scheduled Tuesday in U.S. District Court in Boston.