LONDON (Reuters) - NATO's new secretary-general Lord Robertson said Thursday he was worried by the U.S. Senate's rejection of a nuclear test ban treaty, but said it had a lot to do with politics and he hoped Americans would reconsider.

``Well, it's a very worrying vote,'' Robertson told BBC radio. ``I think it has a lot to do with the partisan nature of American politics at the moment and the sort of febrile atmosphere that comes with a presidential election on the horizon.''

Robertson, who stepped down as Britain's defense minister this week to take up his NATO post, said supporters of the treaty, which was rejected by the U.S. Senate Wednesday, would not give up trying to persuade the Americans that it was in their interests to ratify it.

``We've got to persuade the American Congress that this is in the interest, not just of international security, but also of the United States, and I hope that we can do that and this is not a permanent position,'' Robertson said.

Robertson recalled that key American allies Britain, France and Germany had appealed to the Senate to ratify the accord banning nuclear testing, and noted that the allies had other problems ahead that they must work on together.

Last week, British Prime Minister Tony Blair, France's President Jacques Chirac and Germany's Chancellor Gerhard Schroeder wrote a joint article in the New York Times appealing to the Senate to ratify the nuclear test ban treaty.

``There's a lot of common problems now bubbling up in the future for all of us which will have to be tackled in a concerted way,'' Robertson said.

``I hope that maybe when we've got over the election fever in the United States the Congress will look again and see that arms control is something that's in everybody's interest and that we really have to press ahead with it,'' he said.

Ratification of the Comprehensive Test Ban Treaty (CTBT) failed in the Senate by a vote of 48 to 51 with one abstention. The Senate's Republican majority overwhelmingly opposed the pact.

It was an embarrassing defeat to the Clinton administration, which had fought for U.S. endorsement of the global accord.

The treaty has been signed by more than 150 countries, but cannot go into force unless 44 nuclear-capable countries, including the United States, ratify it.

All five declared nuclear powers -- the United States, Russia, Britain, France and China -- have signed the treaty, but only Britain and France have ratified it.