In a rare rebuke of an ally, the Bush administration announced yesterday that it will cut $18 million in military and economic aid to the authoritarian government of Uzbekistan because it has failed to take a series of promised steps to improve its human rights record.

The decision will not affect funding Uzbekistan receives from the Nunn-Lugar project to secure nuclear weapons material. Programs that support democracy groups and health care will also be exempt.

State Department officials, who had been warning President Islam Karimov's government for months that the additional aid package was in jeopardy, said they hope the move will send a tough message that political repression can be costly.

President Bush reached out to Uzbekistan one week after the Sept. 11, 2001, attacks, noting in a speech that Uzbek militants with links to al Qaeda were a threat. Shortly after, Washington won the rights to a military base on Uzbekistan's border with Afghanistan and aid was promised to Karimov's government.

But Congress, concerned about the country's human rights record, conditioned the new money on substantial and continuing progress in meeting human rights commitments Karimov made during a visit to Washington in 2002.

Among the steps expected were the introduction of free and fair elections, a free press, economic reforms and an end to torture in prisons.

Uzbekistan received the certification several times afterward, but in January the State Department said Uzbekistan had failed to meet international human rights standards. The move was symbolic but was considered a warning to the Central Asian power that its relationship with Washington could suffer.

With yesterday's announcement, Secretary of State Colin L. Powell officially determined that Uzbekistan was not meeting the criteria set by Congress to secure the funds.

"This decision does not mean that either our interests in the region or our desire for continued cooperation with Uzbekistan has changed," State Department spokesman Richard Boucher said in a statement last night. At the same time, he said, "enhanced progress in democratization, respect for human rights and economic reforms are essential for Uzbekistan's security and long-term prosperity, as well as to reinforce a solid and enduring relationship with the United States."

Human Rights Watch analyst Tom Malinowski, who has chronicled Uzbekistan's record, welcomed the latest move as an important victory for human rights.

"This is the first time that the administration has allowed a lack of progress on human rights to have a significant impact on its relationship with a critical security partner in that part of the world," he said.

According to the latest State Department report on human rights around the world, Uzbekistan "remained very poor, and it continued to commit numerous serious abuses." The police and the National Security Service, a successor to the KGB, were cited for committing serious human rights abuses, and the report noted that as many as 5,800 people may be imprisoned for religious and political affiliations.

"The Uzbek government has repeatedly tried to exploit the war on terror to win American sympathy for its crackdown on dissent," Malinowski said. "But the United States isn't buying it because there's a recognition here that when governments like Uzbekistan shut down legitimate dissent, they drive dissenters underground and potentially into the arms of more radical and violent groups. That hurts, not helps, the war on terror."