The BBC's Rob Watson: "The problem is the quesrtion"

In his most specific comments to date on the subject, Mr Bush said he had ''made some mistakes'' more than 20 years ago.

But the son of former President George Bush stopped short of saying whether he had actually taken any illegal drugs.

And he became visibly irritated by questions on the subject at a press conference this week.

The BBC's Paul Reynolds: "Mr Bush is irritated by drugs questions"

However, he said he could have passed stringent background checks for illegal drug use when his father was president, from 1989-1993.

"Not only could I have passed in today's White House, I could have passed the standards applied under the most stringent conditions when my dad was president, a 15-year period,'' he added.

"Over 20 years ago, I did some things ... I made some mistakes and I learned from those," added Mr Bush, a former heavy drinker who is now teetotal.

His spokeswoman Mindy Tucker said Mr Bush was saying he had not done illegal drugs at any time since 1974, when he was 28.

'Absurd rumours'

The drugs issue raised its head as Mr Bush, 53, toured a youth centre in Texas. It was the second day he had been quizzed on the subject.

President Bill Clinton: I didn't inhale

But Mr Bush, who won last week's unofficial Iowa poll for a Republican presidential candidate, insisted such personal issues had no place in the race for the White House.

He said rumours about his personal life were "ridiculous and absurd" and possibly planted by political opponents.

"I'm going to tell people that I made mistakes and that I've learned from those mistakes,'' he added.

''If they like it, I hope they give me a chance, and if they don't like it, they can find somebody else to vote for."

Professor Bruce Buchanan of the University of texas talks about the George Bush drug issue

Mr Bush dodged specific questions, but said that, if he became president, he would sign a statement to say he had not taken drugs for seven years, as is required of federal workers seeking high security clearance.

Clinton

President Clinton, while seeking the White House in 1992, also faced questions about drug use.

He confessed to experimenting with marijuana, but famously remarked: "I didn't inhale''.

The Associated Press said both Democrat presidential hopefuls - Vice President Al Gore and former Senator Bill Bradley - had admitted trying marijuana.