Some supporters have advocated radical action, such as a pitch invasion at Cardiff's Millennium Stadium, but fans' groups fear a major incident would be a huge own goal for the club at English soccer's showpiece occasion.

"One of the core issues for United fans is that Glazer will show no respect to our club's history and tradition, so it would be remiss of fans to do anything that could taint such an intrinsic part of English football's tradition," the groups said in a statement.

Fans opposed to Glazer, who is paying 790 million pounds ($1.5 billion) for United, say he knows nothing about football and will cream off the profits of the world's richest soccer club to pay off his huge debts in purchasing the club.

"We are asking for fans to wear black to mark the death of our club and regard this match as the last to be played whilst the spirit of Manchester United was still alive," said Colin Hendrie of the Independent Manchester United Supporters Association.

A coalition of supporters' groups including IMUSA has issued a statement calling for peaceful protest at the game. Fans burned Glazer's effigy and stopped traffic in Manchester after the takeover was announced last week.

"The supporters' coalition wishes to make clear that it has no intention of encouraging disruption of the match itself.

"The coalition urges United supporters to continue the on-going successful campaign of boycotting United's key commercial backers."

South Wales Police said they had no special policing plans for the match. "If people do protest in an unlawful manner we will respond appropriately," a spokesman said.

"The FA Cup is no different to any other occasion in which people act unlawfully.

"As for any demonstrations, South Wales Police has a long experience of allowing people to express their views is a lawful manner and the FA Cup final will be no exception," a statement from Chief Superintendent Graham Davies, the force's operations manager, said.

Manager Alex Ferguson, in charge at United since 1986, asked for total focus on the match and called for "a united front on Saturday, players and supporters together, to win this cup".

United, the holders of the cup, have failed to win the league title for the past two season and Ferguson's future at Old Trafford is uncertain following Glazer's takeover.

They will not want the 2005 final to be remembered for the wrong reasons. In 1999-2000 they opted out of defending the trophy to take part instead in a club world championship in Brazil, a decision widely condemned in England.