With no perceptible opposition from the Obama administration, Congress has quietly downscaled Washington’s ambitions for the final year of the Afghan war, substantially curtailing development aid and military assistance plans ahead of the U.S. troop pullout.

As congressional appropriators put the final touches on a huge spending bill in recent weeks, they slashed Afghanistan development aid by half and barred U.S. defense officials from embarking on major new infrastructure projects. After making a bid last year for $2.6 billion worth of “critical” capabilities such as mobile strike vehicles for Afghan security forces, the Pentagon agreed it could do with just 40 percent of what it had sought.

The Obama administration had long hoped to bring the Afghan war to a dignified conclusion this year and viewed the president’s State of the Union speech Tuesday as an opportunity to describe the end of America’s longest war as a foreign policy success. But Washington’s appetite to remain engaged in Afghanistan appears to be eroding precipitously, in large part because of how poisonous its relationship with the country’s president has become.

The prevailing sentiment in Washington toward President Hamid Karzai, who has thus far refused to sign a security agreement that would keep U.S. troops and funding in Afghanistan beyond 2014, was even codified in the Afghan portion of the spending bill, which was drawn up without significant public debate.

“The bill prohibits the obligation or expenditure by the United States government, of funds appropriated in this or any other act, for the direct personal benefit of the President of Afghanistan,” appropriators wrote, an unprecedented move that President Obama signed into law last week.

U.S. officials said the cuts and restrictions might appear starker than they actually are because agency heads will retain significant flexibility to use unspent funds from previous years or draw from other sources. But many see the reductions as the unmistakable end of an era of wartime largesse.

“I think this reflects a congressional mood and will have an impact on the ultimate levels of support,” James F. Dobbins, the U.S. special representative for Afghanistan and Pakistan, said in an interview.

Referring to Karzai’s position on a security agreement, Dobbins said, “This is an example of the price Afghanistan is paying for delay.”

Overall, the cost of the Afghan war will not decline substantially this year. Congress set aside $85.2 billion for military operations, roughly the same amount as last year. Although the number of U.S. troops has dropped considerably over the past year, the cost of the war remains high because shutting down bases and moving equipment back to the United States is expensive.

Lawmakers allocated $1.1 billion for assistance to Afghanistan, 50 percent of the $2.1 billion the Obama administration sought, which would have kept spending at the same level as last year.

White House spokeswoman Laura Lucas Magnuson said that even with the reductions in funding, Washington will “continue to provide Afghanistan with significant levels of assistance.”

“We believe that sustained, significant support for Afghanistan’s government and its people is critical to maintaining the gains of the past decade and ensuring that terrorists are never again able to use Afghan soil to attack the homeland,” she said in an e-mailed statement.

America’s multibillion-dollar effort to reconstruct Afghanistan has become increasingly controversial in recent years due to slipping support for the war, rampant corruption in Afghanistan and myriad examples of poorly conceived and shoddily built projects.

On Friday, the special inspector general for Afghanistan reconstruction issued a critical audit of the State Department’s $223 million initiative to bolster the rule of law in Afghanistan. The report said that after contractors were unable to deliver on their promise to implement a nationwide case management system for the courts, they altered the contract to say it would be operational in only seven provinces.

“Unfortunately, waste, fraud and abuse has too often been the result when it comes to the billions we’ve spent in Afghanistan,” Sen. Claire McCaskill (D-Mo.), chairman of the Homeland Security and Governmental Affairs Committee’s subcommittee on financial and contracting oversight, said in a statement.

That sentiment, which several members of both parties have come to share, led appropriators to insist that the Defense Department launch no new infrastructure projects this year. In a memo justifying the decision, appropriators said House members demanded the language, citing the Pentagon’s “lack of a detailed strategy” for such projects.

The Pentagon will “re-evaluate” its plans for the Afghanistan Infrastructure Fund in light of the new restrictions, said Cmdr. Elissa Smith, a Defense Department spokeswoman. She said officials remain hopeful they will still manage to leave behind two hydropower plants to supply electricity to residents of the southern city of Kandahar.

Last year, Pentagon officials submitted to Congress a list of weapons, aircraft and tools that they wanted for Afghan forces, including mobile strike vehicles, night-vision technology, artillery launchers and technology to detect explosives. As the budget was being drawn up, defense officials winnowed the list of items they initially described as “critical” by 60 percent.

Smith said aircraft were among the items removed, but the Pentagon did not provide a detailed list. The reassessment was done after Afghan forces had completed their first year in the lead of combat operations, taking into account estimates of how much U.S. hardware the Afghans would be able to maintain after U.S. troops withdraw, Smith said.

U.S. military officials are wrestling with that question as the impasse over the security agreement drags on. In recent days, the Pentagon told the White House it should strive to keep a force of at least 10,000 to continue training the Afghans and conducting counterterrorism missions. The military said it would rather pull out altogether than keep a smaller force.

“That is not a future we are seeking, and we do not believe that is in Afghanistan’s interests,” White House spokeswoman Caitlin Hayden said in an e-mail, referring to the prospect of a full pullout. “The further this slips into 2014, however, the more likely such an outcome is.”

Officials at the U.S. Agency for International Development said the level of funding appropriated this year is unlikely to have an immediate impact on its core efforts: providing disaster relief and building the country’s education and health-care sectors.

Larry Sampler, who heads the agency’s Afghanistan projects, said USAID could cope with the cuts because of generous funding in earlier years. Money for major projects already underway is being held in escrow accounts from previous appropriations, including $400 million for an electrical project and $70 million to $80 million for the Kajaki dam in Kandahar province.

In the future, however, USAID will get out of the business of big infrastructure projects such as building roads and focus on smaller, more tailored initiatives to build up fledgling institutions.

“I’m not shooting for an Afghanistan that’s another Switzerland,” said Sampler. “I’m hoping for an Afghanistan that’s a Bangladesh. It’s struggling, but it’s improving.”