* Falklands still source of tension 30 years after war
* Ambassador described PM as "foolish" and "dumb"
By Andrew Osborn
LONDON, Aug 21 (Reuters) - Britain asked Argentina's ambassador to clarify remarks about Prime Minister David Cameron on Wednesday after she described his handling of a long-running dispute over the contested Falkland Islands as "foolish" and him as "dumb".
In the latest twist in an ill-tempered feud between the two countries over the South Atlantic archipelago, Britain's foreign office said it was seeking confirmation of what the ambassador, Alicia Castro, had said.
"If true, these comments are undiplomatic," a Foreign Office spokeswoman told Reuters. "We are seeking confirmation of what was said with the Argentine Embassy. Our policy towards the Falkland Islands has not changed and will not change."
Referring to a referendum in March in which residents were asked if the islands should remain a British Overseas Territory, a source from Cameron's office added: "We don't think it's foolish to listen to 99.8 percent of the population, who have made it very clear that they want to stay British."
The contested islands, known as Las Malvinas by Argentines, remain a source of tension between London and Buenos Aires more than 30 years after Argentina unsuccessfully invaded them in an attempt to assert its sovereignty claim.
On Tuesday, Castro told Argentine lawmakers that Cameron had unwisely publicised comments about the Falklands by former Buenos Aires Archbishop Jorge Bergoglio, made before he was named pope earlier this year.
"Prime Minister Cameron was dumb, if I may use the word dumb before Congress," Castro said during a hearing of the Senate Foreign Relations Committee, pausing to laugh.
"When the pope was named I asked one of our people to look into what Bergoglio had said regarding the Malvinas. Cameron did the same and was foolish enough to disseminate the information," she added.
Cameron said in March that the pope had been wrong to say in 2012 that Britain had "usurped" the islands.
In April, Castro declined an invitation to attend the funeral of former Prime Minister Margaret Thatcher who led Britain at the time of the 1982 Falklands war.
Memories of that conflict remain raw and Argentine President Cristina Fernandez has mounted a campaign to renegotiate the islands' sovereignty, lobbying Pope Francis on the issue and rejecting the results of the islands' referendum.
The Argentine Embassy declined immediate comment, saying it planned to issue a statement on Castro's remarks. (Editing by Alison Williams)