Republican presidential candidate John McCain says he will emphasise national security issues from Afghanistan to global climate change on a visit to Europe and the Middle East next week.

McCain, who will be his party's presidential nominee to face the Democrats' choice in the November election, will visit Israel, Britain and France as part of a congressional delegation.

He will be joined by two of his closest Senate allies, Democrat-turned-Independent Joe Lieberman of Connecticut and South Carolina Republican Lindsey Graham.

McCain told reporters on his campaign bus on Wednesday that while many in Europe might want to take his measure as a potential president, he was going as a ranking member of the Senate Armed Services Committee, not as a candidate.

"I won't be offering them my vision because I'm going as a member of the Armed Services Committee, not as the nominee of our party," said McCain, who at 71 would be the oldest person ever elected to a first presidential term.

Still, the visit gives him an excuse to grab some headlines and television news time that is otherwise being taken up by the fierce Democratic contest between Illinois Senator Barack Obama and New York Senator Hillary Clinton.

While riding in his bus from New Hampshire to Boston, McCain sometimes gazed overhead at a television showing the Fox News Channel and saw the Democrats dominating coverage with occasional snatches of himself on the screen.

He said he would avoid politics on his trip "by not talking politics, only talking national security".

McCain has had notable differences with President George W Bush on a host of issues although both are from the same political party.

He is a stronger advocate than Bush on taking steps to control global warming. He also disagreed for a long time with US strategy in Iraq, believes the United States should shut down the military prison at Guantanamo Bay, Cuba, where terrorism suspects are held, and battled Bush on the issue of torture.

"There are obvious differences," said McCain. But, he said, "I certainly won't articulate them overseas."

McCain and his colleagues will hold talks with Israeli, British and French leaders. A side trip to Iraq is possible. He has met both British Prime Minister Gordon Brown and French President Nicolas Sarkozy in the past.

"I know these people. It's not as if they're seeing an unknown quantity. It's not the leaders taking measure - maybe people will in those countries, but the leaders I have strong relationships with."

McCain said he expected Brown in particular to talk about climate change, an issue that former Prime Minister Tony Blair brought to the fore.

McCain has said in the past he believes the United States and its allies should adopt a "cap and trade" system of capping greenhouse gas emissions, a step the Bush administration opposes.

"They (European leaders) do view climate change as a national security issue," said McCain.

On the same bus ride, Lieberman said he expected European leaders would want to talk about the possible expansion of NATO and relations with Russia.

The Russian Government of Vladimir Putin has voiced concern about expanding NATO to countries in the former Soviet empire.