LONDON (Reuters) - The treasurer of the Conservative Party under former Prime Minister Margaret Thatcher on Friday denied allegations he had sexually abused children in the 1970s and 1980s and warned he may sue to protect his reputation.

Lord Alistair McAlpine, who served as party treasurer from 1975 to 1990, said in a statement that he had been named by ill-informed commentators on the Internet and in the media as the unidentified man accused by one pedophile victim of abusing children in social care.

"Even though these allegations made of me by implication in the broadcast and print media, and made directly about me on the internet, are wholly false and seriously defamatory I can no longer expect the broadcast and print media to maintain their policy of defaming me only by innuendo," he said.

"I therefore have decided that in order to mitigate, if only to some small extent, the damage to my reputation I must publicly tackle these slurs and set the record straight," he said.

"In doing so I am by no means giving up my right to sue those who have defamed me in the recent past or who may do so in the future."

The abuse claims, which follow the unmasking of late BBC star presenter Jimmy Savile as one of Britain's most prolific sex offenders, had stoked concern that a powerful pedophile ring may have operated in Britain in the 1970s and 1980.

That could have proven damaging to Prime Minister David Cameron's party - which rules in an uneasy coalition with centrists - and tarnished the image of the era of Margaret Thatcher, prime minister from 1979 to 1990.

Cameron ordered an investigation this week after Steven Messham, one of hundreds of victims of sexual abuse at children's care homes in Wales over two decades, said in an interview aired by the BBC that a prominent member of the Conservative party had abused him during the 1970s.

That provoked a wave of speculation on social media sites and in the UK media that McAlpine was one of the suspected Conservative politicians.

"I am, as is now well known to readers of the internet and to journalists working for the print and broadcast media, one of the individuals implicated by Mr Messham," McAlpine said. "I did not sexually abuse Mr Messham or any other residents of the children's home in Wrexham."

"Any abuse of children is abhorrent but the sexual abuse to which these vulnerable children were subjected in the 1970's and 1980's is particularly abhorrent," he said.

(Reporting by Guy Faulconbridge; editing by Ralph Boulton)