Ministers said Canada had yet to decide whether to join the national missile defence system, which emerged as a political hot potato during the country's recent general election campaign.

The United States and Canada earlier announced they had extended the North American Aerospace Defense Command aerospace warning function to support missile defense.

The deal allows the command, known as NORAD, information on incoming missiles to be used by the future US missile defense program.

Foreign Minister Pierre Pettigrew said it made "good sense to amend the agreement so that this essential NORAD function can be preserved and Canada can continue to benefit from the security it provides to our citizens."

"This amendment safeguards and sustains NORAD regardless of what decision the government of Canada eventually takes on ballistic missile defense."

Defense Minister Bill Graham told reporters the move did not "affect or in any way determine the ultimate decision as to whether Canada will participate in missile defense."

Washington, keen to press on with constructing the missile defense system, a key plank of the Bush administration's defense policy, has been pressing Canada for a decision for over a year.

But the Canadian government has had to walk a political tightrope on the issue.

Advocates of the scheme say a decision not to take part would badly damage the country's prestige and make Canada largely irrelevant in the defense of its own continent.

But ministers realise that the scheme is highly unpopular in Canada, as is the Bush administration which is building it.

Ministers have relied on the tortuous position that they oppose any system that involves the "weaponization of space" -- a position observers say does not rule out current US plans for missile defense.

US State Department spokesman Richard Boucher said Washington looked forward to "continuing this longstanding defense cooperation" through NORAD.

The new deal "formally assigns" to NORAD the responsibility for providing the threat information under the missile defense mission, Boucher said.

Missile defense meanwhile thrust itself to the top of Secretary of State Colin Powell's agenda.

Powell was due to leave the US capital early Friday for a one-day trip to Greenland to sign a series of pacts intended to modernize a US military base which will support the missile defense program.

He will meet Danish Foreign Minister Per Stig Moeller and Greenland Deputy Premier Josef Motzfeldt to sign agrrements paving the way for an upgrade of radar facilities at Thule Air Base which will support the US missile defense program.

Thule served as a key listening post during the Cold War and is now considered essential to US missile defense plans.

As compensation to Greenland, where there was much opposition to the modernization and expansion plans, Copenhagen and Washington are to renew a 1951 treaty with Greenland recognizing it as an autonomous Danish territory.

WAR.WIRE