WASHINGTON » As a growing chorus of New York politicians joined the opposition to a Manhattan trial for the accused Sept. 11 conspirators, a White House spokesman said on Thursday that President Barack Obama still believed a civilian criminal trial for them could be held “;successfully and securely in the United States of America.”;

The dispute over a trial location, touched off when Mayor Michael R. Bloomberg of New York complained of costs and disruption, threatened to reopen the divisive question of how those accused of plotting the murder of more than 3,000 Americans should be brought to justice.

Republicans in the Senate and House said they would try to block funding for civilian criminal trials for the alleged terrorists, seeking to force the administration to place them on trial before a military commission in Guantanamo Bay, Cuba, or on a military base elsewhere.

Opponents of civilian trials said they hoped new doubts about a New York trial and increased fears of terrorism since the attempted airliner bombing on Christmas Day would win more Democratic support for such measures.

The apparent collapse of what had seemed since November to be a settled decision to hold the trial in lower Manhattan was clear when New York's senior senator, Charles E. Schumer, said Thursday that he was encouraging the Obama administration “;to find suitable alternatives.”;

A Schumer spokesman, Brian Fallon, said the senator was “;following the guidance”; of Mayor Bloomberg and New York Police Commissioner Raymond W. Kelly and “;shares their concerns about costs, logistics and security.”;

Obama reiterated his support for a civilian trial, which supporters say would have greater legitimacy than a military tribunal. A White House spokesman, Bill Burton, called Khalid Shaikh Mohammed, the self-described 9/11 mastermind, “;a murderous thug”; and said “;the president is committed to seeing that he's brought to justice.”;

Burton said the president agreed with Attorney General Eric H. Holder Jr. that civilian trials are the right choice. “;Currently our federal jails hold hundreds of convicted terrorists, and the president's opinion has not changed on that,”; he said.

But Obama is leaving the choice of locations to the Justice Department, Burton said.

Finding a site for a trial rejected by New York City, however, could prove a challenge. Other Southern District locations, including military bases, appeared to pose problems. Some officials mentioned the Eastern District of Virginia, where terror trials have been held, or the unused Illinois prison where the administration has proposed to move detainees from Guantanamo.

A Justice Department spokesman, Dean Boyd, said Thursday night that there had been no decision to shift the trial from Manhattan. He said Justice Department officials were confident that the Southern District, where the department's most experienced terrorism prosecutors work, could handle the case “;while minimizing disruptions to the community to the greatest extent possible consistent with security needs.”;

City officials have estimated security and logistical costs could total more than $200 million per year for a trial that could last several years, and some politicians have complained that a trial could make the city an even more attractive target for al-Qaida.

Bloomberg, who in November had strongly backed Holder's decision to bring the 9/11 defendants to the city they were accused of attacking, surprised administration officials on Wednesday by saying he had changed his mind. On Thursday, he elaborated, not closing the door to a Manhattan trial but expressing strong preference for another location.

The mayor said “;there are places that would be less expensive for the taxpayers and less disruptive”; than New York City. “;For example,”; he said, “;military bases away from central cities where it is easier to provide security at much less cost.

“;And so, would I prefer that they did it elsewhere? Yes, but if we are called on, we will do what we're supposed to do,”; Bloomberg said.

Also on Thursday, Gov. David A. Paterson repeated his longstanding opposition to a Manhattan trial, and several more politicians expressed doubts or outright opposition.

New York's junior senator, Kirsten E. Gillibrand, a Democrat, agreed and said she was “;open to alternative locations,”; adding that she remained committed to a federal criminal trial. And eight elected officials from Manhattan wrote to Holder to say a trial in the borough would be “;extremely burdensome.”;

They said they back a criminal trial but asked for a review of other possible sites in the Southern District of New York, which includes Manhattan, the Bronx and six counties north of the city.

In Washington, congressional Republicans who have long opposed criminal trials said they hoped to use the debate over trial locations to steer the cases back to military commissions.

Rep. Peter King, D-N.Y., introduced legislation on Wednesday that would block funding for civilian trials for the Sept. 11 plotters, and Sen. Lindsey Graham, R-S.C., said he would introduce a parallel bill in the Senate next week.

Graham, an experienced military prosecutor who has long argued that foreign terrorists should be treated as enemy combatants, proposed a similar amendment in November but it failed to pass the Senate by 54-45. He said he believed the same measure could pass today.

But the administration is anything but eager to reopen a debate over whether civilian or military trials were the right choice. Other Southern District sites come with their own problems.

Among the sites mentioned are Stewart Air National Guard Base near Newburgh and a federal prison at Otisville. But the base has no court or prison facilities, and the prison has no courtroom, their spokesmen said.

Another possibility might be the federal courthouse in White Plains, 30 miles north of Manhattan, with a population of more than 50,000. But the city's mayor, Adam T. Bradley, said he had deep concerns about security.

“;I think we need to be realistic,”; he said. “;Once you've placed it in a place like White Plains, you've made the city an automatic target, and everything located in it.”;