Moreover, a demolition project would have required the tower walls to be opened on dozens of floors, followed by the insertion of thousands of pounds of explosives, fuses and ignition mechanisms, all sneaked past the security stations, inside hundreds of feet of walls on all four faces of both buildings. Then the walls presumably would have been closed up.

All this would have had to take place without attracting the notice of any of the thousands of tenants and workers in either building; no witness has ever reported such activity. Then on the morning of Sept. 11, the demolition explosives would have had to withstand the impacts of the airplanes, since the collapse did not begin for 57 minutes in one tower, and 102 minutes in the other.

Those who believe in the demolition theory remain unpersuaded by government statements new or old, and the officials who issued the would-be rejoinders say they are not surprised. “We realize that this fact sheet won’t convince those who hold to the alternative theories that our findings are sound,” Mr. Newman said. “In fact, the fact sheet was never intended for them. It is for the masses who have seen or heard the alternative theory claims and want balance.”

Mr. Newman was correct that the institute’s reports would not convert those who favor the demolition theories, said Kevin Ryan, who is the coeditor of an online publication, www.journalof911studies.com, that has published much of the material arguing that the government’s accounts are false.

“The list of answers NIST has provided is generating more questions, and more skepticism, than ever before,” Mr. Ryan said.

Mr. Newman said, “NIST respects the opinions of others who do not agree with the findings in its report on the collapses of WTC1 and WTC2.”

The State Department report, which officials said was written independently of the new institute study, is titled, “The Top Sept. 11 Conspiracy Theories” and says, “Numerous unfounded conspiracy theories about the Sept. 11 attacks continue to circulate, especially on the Internet.” Produced by an arm of the State Department known as a “counter-misinformation team,” the report is dated Aug. 28 and appears as a special feature on the department’s Web site, at http://usinfo.state.gov/media/misinformation.html.