Martinez said he passed along the ``now-infamous memo'' to Sen. Tom Harkin, D-Iowa, assuming it was an official summary of talking points on the Schiavo bill introduced by Martinez rather than a memo listing the political reasons to support the legislation.

``Senator Harkin asked me for background information on the bill,'' the senator said. ``I took a copy of what I believed to be my one-pager on `The Incapacitated Persons Legal Protection Act' from my lapel and gave it to him.

``Unbeknownst to me, instead of my one-pager on the bill, I had given him a copy of the now-infamous memo that at some point along the way came into my possession.''

The aide, identified as senior counsel Brian Darling, offered to resign. Martinez, who said in a statement that ``this is in no way how I intend to conduct my business as a United States senator,'' accepted.

``I vehemently condemn this memo's sentiments,'' Martinez said, adding that the memo ``in no way reflected my motivations for being involved in this legislation.''

The memo included language from a Martinez news release on the Schiavo case but in other ways was strikingly different: It contained eight talking points and urged Republicans to intervene because the Schiavo case was ``a great political issue.''

Circulated among Republicans and divulged to ABC News during the Schiavo debate, the document specifically noted that the issue could be used against Florida Democrat Bill Nelson, up for re- election in the Senate in 2006.

Its origin had been a hot Capitol Hill mystery, initially proving an embarrassment to Republicans. It prompted some Republicans to suggest Democrats had concocted it as a dirty trick.

Its authenticity questioned, the memo - described on ABC and in other publications including The Washington Post and The Tampa Tribune after Democrats provided copies - soon became a cause celebre among conservative bloggers on the Web.

But Senate staff members working at the request of Sen. Frank Lautenberg, D-N.J., had failed after days to determine the origin or author.

``I apologize to my old friend, Senator Nelson,'' Martinez said Wednesday night.

The memo, he said, ``was not approved by me or any other member of my staff.''

He said his senior aide was ``unilaterally responsible.''

Darling, a former lobbyist on gun rights and member of the Bush-Cheney recount team in Florida in the 2000 presidential election, could not be reached for comment.

Reporter Keith Epstein can be reached at (202) 662- 7673.