WASHINGTON — The legal counsel to Sen. Mel Martinez, R-Fla., admitted yesterday that he was the author of a memo citing the political advantage to Republicans of intervening in the Terri Schiavo case, the senator said last night.

Brian Darling, a former lobbyist for the Alexander Strategy Group on gun rights and other issues, offered his resignation, and it was immediately accepted, Martinez said.

The senator said aides had assured him earlier that his office had nothing to do with producing the memo. "I never did an investigation, as such," he said. "I just took it for granted that we wouldn't be that stupid. It was never my intention to in any way politicize this issue."

Martinez, a freshman who was secretary of Housing and Urban Development for most of President Bush's first term, said he had not read the one-page memo. He said he inadvertently passed it to Sen. Tom Harkin, D-Iowa, who had worked with him on the issue. Other Senate aides then gave the memo to reporters for ABC News and The Washington Post.

Harkin said in an interview that Martinez handed him the memo on the Senate floor, in hopes of gaining his support for the bill that gave federal courts jurisdiction in an effort to restore Schiavo's feeding tube. "He said these were talking points, something that we're working on here," Harkin said.

The mystery of the memo's origin had roiled the Capitol, with Republicans accusing Democrats of concocting the document as a dirty trick, and Democrats accusing Republicans of trying to duck responsibility for exploiting the dying days of a brain-damaged woman.

Conservative Web logs have challenged the authenticity of the memo.

The unsigned memo, which initially misspells Schiavo's first name, includes eight arguments for the bill and calls the controversy "a great political issue."

"This legislation ensures that individuals like Terri Schiavo are guaranteed the same legal protections as convicted murderers like Ted Bundy," the memo concludes.

It asserts that the case would appeal to the party's core supporters, saying, "This is an important moral issue and the pro-life base will be excited that the Senate is debating this important issue," and suggests that the issue could damage Martinez's fellow Florida senator, Democrat Bill Nelson, in the 2006 elections.

In a statement last night, Martinez said Harkin asked him for background information on the bill and that he gave him what he thought was a routine, one-page staff memo. "Unbeknownst to me, instead of my one page on the bill, I had given him a copy of the now infamous memo," the statement said.

Harkin said he thought the politics argument was "rather out of line," but said he did not discuss the matter with Martinez. Harkin said he has no complaints about Martinez.

In other developments:

Senate hearing: The Senate Health, Education, Labor and Pensions Committee held a hearing yesterday on the quality of hospice care and the legal needs of disabled people. The committee originally had tried to call Terri Schiavo and her husband, Michael, before it on March 28. Instead, it heard yesterday from experts on end-of-life issues, brain injuries and discrimination against disabled people to determine if legislation might be needed for cases such as Schiavo's.

Death threat: A California woman has been charged with threatening to kill Michael Schiavo. The federal charge against Dera Marie Jones, 32, stems from a posting on an America Online message board: "If she dies I will kill Michael Schiavo and the judge. This for real!"

Information on the Senate hearing and threat against Michael Schiavo were reported by The Associated Press.