ONDON, Feb. 7 — The British government admitted today that large sections of its most recent report on Iraq, praised by Secretary of State Colin L. Powell as "a fine paper" in his speech to the United Nations on Wednesday, had been lifted from magazines and academic journals.

But while acknowledging that the 19-page report was indeed a "pull-together of a variety of sources," a spokesman for Prime Minister Tony Blair defended it as "solid" and "accurate."

The document, "Iraq: Its Infrastructure of Concealment, Deception and Intimidation," was posted on No. 10 Downing Street's Web site on Monday. It was depicted as an up-to-date and unsettling assessment by the British intelligence services of Iraq's security apparatus and its efforts to hide its activities from weapons inspectors and to resist international efforts to force it to disarm.

But much of the material actually came, sometimes verbatim, from several nonsecret published articles, according to critics of the government's policy who have studied the documents. These include an article published in the Middle East Review of International Affairs in September 2002, as well as three articles from Jane's Intelligence Review, two of them published in the summer of 1997 and one in November 2002.

In some cases, the critics said, parts of the articles — or of summaries posted on the Internet — were paraphrased in the report. In other cases, they were plagiarized — to the extent that even spelling and punctuation errors in the originals were reproduced.

The Blair government did not deny that any of this had happened. But its spokesman insisted today that the government believed "the text as published to be accurate" and that the document had been published because "we wanted to show people not only the kind of regime we were dealing with, but also how Saddam Hussein had pursued a policy of deliberate deception."

He added: "In retrospect, we should, to clear up any confusion, have acknowledged which bits came from public sources and which bits came from other sources." He said the document had been written by government officials and drawn from "a number of sources, including intelligence sources."

"The overall objective was to give the full picture without compromising intelligence sources," he said.

But critics of the government said that not only did the document appear to have been largely cut and pasted together, but also that the articles it relied on were based on information that is, by now, obsolete.

For instance, the second section of the three-part report, which is described on the Downing Street Web site as providing "up-to-date details of Iraq's network of intelligence and security," was drawn in large part from "Iraq's Security and Intelligence Network: a Guide," an article about the activities of Iraqi intelligence in Kuwait in 1990 and 1991, which appeared in the Middle East Review of International Affairs last September. Its author was Ibrahim al-Marashi, a postgraduate student at the Monterey Institute of International Studies in California.

Mr. Marashi told Channel 4 News, which first reported the plagiarism charges, that his research had been drawn primarily from two huge sets of documents: "one taken from Kurdish rebels in the north of Iraq — around four million documents — as well as 300,000 documents left by Iraqi security services in Kuwait." He also said that while he had no reason to doubt the truth of anything he had written and believed the government report to be accurate, no one had asked permission or informed him about using his work.

"I am surprised, flattered as well, that this information got used in a U.K. government dossier," Mr. Marashi said in an interview with Reuters. "Had they consulted me, I could have provided them with more updated information."

Dr. Glen Rangwala, a lecturer in politics at Cambridge University who has compared the British report with the articles it used as sources, said that in some cases, the authors apparently changed phrases from the original articles to make the case against Iraq seem more extreme.

For instance, Dr. Rangwala said, a section on the Mukhabarat, the Iraqi directorate of general intelligence, appeared to have been lifted verbatim from Mr. Marashi's article, except for a few tweaks. Where Mr. Marashi mentions that the Mukhabarat's responsibilities include "monitoring foreign embassies in Iraq," the government document speaks of "spying on foreign embassies in Iraq." Mr. Marashi's description of the Mukhabarat's role in "aiding opposition groups in hostile regimes" becomes "supporting terrorist organizations in hostile regimes."

Critics of the British and American policy toward Iraq said the report showed how little concrete evidence the two governments actually have against Iraq, as well as how poor their intelligence sources were.

"Both governments seem so desperate to create a pretext to attack Iraq that they are willing to say anything," said Nathaniel Hurd, a consultant on Iraq and a critic of the American position. "This U.K. dossier, which deceptively uses outdated material and plagiarizes, is just the latest example of official dishonesty."

Opposition politicians here attacked the report as the deceptive work of a bumbling government clutching at straws as it tries to make a case for war.

"This is the intelligence equivalent of being caught stealing the spoons," said Menzies Campbell, the foreign affairs spokesman for the Liberal Democrats. "The dossier may not amount to much, but this is a considerable embarrassment for a government trying still to make a case for war."

Bernard Jenkin, the Conservative Party's shadow defense secretary, said the government had not satisfactorily addressed the concerns raised by the disclosures.

"The government's reaction utterly fails to explain, deny or excuse the allegations," Mr. Jenkin said. "The document has been cited by the prime minister and Colin Powell as the basis for a possible war. Who is responsible for such an incredible failure of judgment?"