The Elgin Marbles came to the UK in 1799
Writing in The Times, Robert Anderson said the Parthenon sculptures are "one of the greatest treasures of the British Museum".
Greece is looking for a loan of the pieces in time for the Athens Olympics in 2004.
Fourteen British MPs, including former sports minister Tony Banks, have called on the UK government to return the marbles and a campaign, Parthenon 2004, will be launched on Wednesday.
'Unbowed'
Actress Janet Suzman told BBC News 24 that it was time for "looser thinking and cultural collaboration".
She said: "Bloody but unbowed the Parthenon still stands sailing above the city of Athens.
"Hopefully when the marbles are loaned back it will be possible to see in situ the two entities joined together.
"The building is bereft of its marbles."
But Mr Anderson told the BBC's Six O'Clock News the marbles "belonged to the British Museum and the international public who come to the British Museum".
Greece has long called for the Parthenon sculptures to be brought back.
A £29m museum is under construction in Athens for their return.
Mr Anderson said that if the marbles were to go into the museum "what would a loan mean?".
He said: "We are a big international museum [and] we are open to the public every day of the year.
"It is extremely important that they remain here in London."
The 56 sculpted friezes were sent to the British Museum after their removal from Greece during Ottoman Turkish rule.
'Defamed'
Known in Greece as the Parthenon sculptures, they date from between 447 and 432 BC and depict the most formal religious ceremonies of ancient Athens - the Panathenaea procession.
In 1799 the British ambassador to the Ottoman Empire, Lord Elgin, removed the friezes and brought them to the UK.
Mr Anderson wrote in The Times that Elgin had been unjustly "defamed" by the campaign to restore the pieces to Greece.
He added that at Elgin's time the Parthenon was a ruin, having been damaged by an explosion at the end of the 17th century.
"We are indebted to Elgin for having rescued the Parthenon sculptures and others from the Acropolis from the destruction they were suffering," he wrote.
In November 2001, poet Titos Patrikios led calls for a return of the pieces.
He is heading a global Cultural Olympiad which runs from 2001 to 2004 as part of the Olympic celebrations.
"It is now a cultural and moral obligation of all of us to reconstruct the unity of important monuments in the world," said Mr Patrikios.
"We cannot continue living with mutilated monuments, especially those which have a symbolic value.
"There are some monuments which are sites of memory. We need historical monuments, not for nationalistic reasons, but for existentialist reasons.
"The Parthenon is a site of memory."
The campaign for their return is being backed by actors including Vanessa Redgrave, Joanna Lumley, Dame Judi Dench and Sir Sean Connery.