WASHINGTON — A group of Russian engineers secretly aided Saddam Hussein's long-range ballistic missile program, providing technical assistance for prohibited Iraqi weapons projects even in the years just before the war that ousted him from power, American government officials say.

Iraqis who were involved in the missile work told American investigators that the technicians had not been working for the Russian government, but for a private company. But any such work on Iraq's banned missiles would have violated U.N. sanctions, even as the U.N. Security Council sought to enforce them.

Although Iraq ultimately failed to develop and produce long-range ballistic missiles and though even its permitted short-range missile projects were fraught with problems, its missile program is now seen as the main prohibited weapons effort that Iraq continued right up until the war was imminent.

After the Persian Gulf War in 1991, Iraq was allowed only to keep crude missiles that could travel up to 150 kilometers, or about 90 miles, but the Russian engineers were assisting Baghdad's secret efforts illegally to develop longer-range missiles, according to the American officials.

Since the invasion in March, American investigators have discovered that the Russian engineers had worked on the Iraqi program both in Moscow and in Baghdad, and that some of them were in the Iraqi capital as recently as 2001, according to people familiar with the intelligence on the matter.

Because some of the Russian experts were said to have formerly worked for one of Russia's aerospace design centers, which remains closely associated with the state, their work for Iraq has raised questions in Washington about whether Russian government officials knew of their involvement in forbidden missile programs. "Did the Russians really not know what they were doing?" asked one person familiar with the U.S. intelligence reports.

A spokesman for the Russian embassy in Washington denied any knowledge of the allegations of recent Russian technical support for Iraq's missile effort.

"The U.S. has not presented any evidence of Russian involvement," said Yevgeny Khorishko, a spokesman for the Russian Embassy.

CIA and White House officials refused to comment on the matter, and people familiar with the intelligence say they believe that the administration has been reluctant to reveal what it knows about Moscow's involvement in order to avoid harming relations with President Vladimir V. Putin.

"They are hyper-cautious about confronting Putin on this," complained one intelligence source.