Neither is happening. In the south, army troops and Marines are bogged down by supply problems and unexpected Iraqi resistance. In the north, 1,000 lightly armed US paratroopers only arrived Wednesday night, not enough to seriously challenge the Iraqi government. The reason is that Turkey, a close NATO ally that shares a 218-mile border with Iraq, earlier this month refused a Bush administration request to permit the armored troop deployment from its soil.

One week into the war, the administration’s inability to win Turkey’s approval has emerged as an important turning point in the US confrontation with Iraq that senior US officials now acknowledge may ultimately prolong the length of the conflict. It is a story of clumsy diplomacy and mutual misunderstanding, US and Turkish officials said. It also illustrates how the administration undercut its own efforts to broaden international support for war by allowing its war plan to dictate the pace of its diplomacy, diplomats and other experts in US-Turkish relations said.

Turkey’s rejection was especially surprising to administration officials because Turkey has loyally backed US military actions since the Korean War a half century ago. In retrospect, US officials say, they made unrealistic demands on the new government of Turkey, which was installed only last November, insisting on a vote that it accept as many as 90,000 US troops even as President Bush was still publicly claiming he had made no decision to attack Iraq. US officials repeatedly set deadlines for action, but then took no action when the deadlines passed, costing the administration credibility and inflating Turkey’s sense of importance.

Some senior officials in Turkey, where 94 percent of the population opposed the war, even began to believe they could halt a military conflict through inaction on the US request. The Turkish prime minister at the time, Abdullah Gul, appeared racked with doubts about a war, and Turkish officials suggest he secretly opposed the American troop request. The deadlines were never real, US officials admit now, but merely a feint to keep pressure on Turkey. The Pentagon augmented the pressure by keeping three dozen ships packed with tanks and heavy equipment for the army’s 4th Infantry Division bobbing off the Turkish coast in the eastern Mediterranean awaiting permission to offload.

When the Turkish government finally agreed to schedule a vote on the US request on March 1, Parliament voted it down.

The State Department and Vice President Dick Cheney’s office both pushed to send the ships to Kuwait to shore up the Marines and other Army forces assembling there for a southern invasion. President Bush, in fact, had warned Turkish officials that the United States did not need a northern front for a successful war, according to a senior administration official.

But the military, in particular Army Gen. Tommy Franks, the head of US Central Command and one of the chief architects of the war plan, clung to the idea that Turkey ultimately would accept the troops, officials said. The Pentagon insisted that administration diplomats press the government in Ankara to reverse the vote.

The ships only started moving through the Red Sea to Kuwait after the war started last week, and the 4th Infantry Division will not be ready to move into Iraq until at least mid-April. “The Turks came to think we would pay anything for their cooperation,’’ a senior US official said. “The Turks got to believe they were indispensable, and it colored their capacity to decide when they had negotiated enough.’’

Yasir Yakis, the former Turkish foreign minister who played a key role in the talks with the United States, was quoted saying as much last week in the newspaper Vatan. “We thought the United States needed the northern front. We made bargaining plans based on this. We did not consider the possibility that they would apply Plan B,’’ he said, using the phrase for an invasion of Iraq without Turkish cooperation.

Turkey’s rejection not only forced a rewrite of the war plan but it undercut the administration’s broader diplomatic efforts to win international support for an invasion. Diplomats said the image of Turkey resisting US pressure emboldened smaller countries on the United Nations Security Council to reject a proposed US-British resolution authorizing military action. The failure of that resolution in turn made it impossible for the United States to recruit such close allies as Canada and Mexico to join the fight against Iraq, since they had tied their support to a second resolution.

Moreover, the impasse seriously damaged US-Turkish relations, administration officials now acknowledge. Turkey was the last NATO ally to grant permission for US warplanes to enter it airspace for the war, and a US special envoy has been in and out of Ankara this week to prevent Turkey from sending its own troops into northern Iraq. Once portrayed as an indispensable ally and the US model for a Muslim democracy, Turkey now finds itself scorned by Washington and in a position to be blamed if the war goes poorly.