Washington ? The United States on Friday began sharing highly sensitive intelligence about Iraq’s weapons programs with the United Nations, as the White House agreed to nearly double the number of U.S. troops in the Persian Gulf region next month, according to U.S. officials.

The Pentagon is preparing to deploy as many as 50,000 troops, bringing the total to almost 100,000, Pentagon officials said.

Both steps will increase the pressure on the regime of Iraqi President Saddam Hussein in preparation for a tough new round of inspections that are set to begin in the new year, according to U.S. and U.N. officials.

The U.S. intelligence shared with U.N. weapons inspectors Friday involves a few sites — less than half a dozen — that are suspected of being connected to chemical weapons production, U.S. officials said.

The hand-over of data is meant to test what happens to information provided by the United States — and to see if it falls into Iraqi hands before U.N. weapons inspectors can check out the facilities, a common problem in the past.

“We’re starting out cautiously,” said a senior U.S. official who requested anonymity.

The new intelligence cooperation began as U.S. officials expressed growing concern about the fate of leading Iraqi scientists.

“We believe Iraq is taking steps to make people unavailable or less available,” a senior administration official said.

Some scientists and engineers involved in the production of nuclear, chemical and biological weapons or ballistic missiles may already have been imprisoned or put under a form of house arrest or protective custody, to cut them off from U.N. inspectors and from defecting, the sources added.

Iraq’s top scientists are the centerpiece in the next phase of inspections, because the United States and the United Nations believe the arms experts can uncover what Washington insists are Iraq’s hidden weapons programs.

On Friday, U.S. officials refused to discuss unconfirmed reports from U.N. diplomats and Iraqi dissidents that almost three dozen key Iraqi arms experts are unaccounted for. At least one report claims that Iraq has issued false death certificates for scientists spirited out of sight.

President Bush and United Nations Secretary General Kofi Annan discuss Iraq Friday in the Oval Office at the White House.

U.S. officials would only confirm their tentative conclusion that some of the Iraqis they want the U.N. teams to interview are likely to be beyond the reach of inspectors.

“We have reports that scientists may have been hidden away, and we believe this is probably true,” said a well-placed official who requested anonymity.

U.N. sources also said they have heard reports of scientists being spirited out of the country, being murdered or going missing but hadn’t yet tested the Iraqis’ ability to produce specific experts.

“Sometimes those who are in jail are the easiest to produce,” said Ewen Buchanan of the U.N. Monitoring, Verification and Inspection Commission.

Iraq has promised to meet the deadline for providing a full list of all personnel connected with its arms industry by the end of the month, Gen. Amar Saadi said Thursday in Baghdad.

The United States and the United Nations are still working out procedures for tracking down and interviewing scientists in January and the sticky issue of what happens to them — and their families — afterward.

President Bush, weighing in for the first time since a U.N. assessment Thursday, said Friday that Iraq’s weapons declaration was not encouraging because it was “a long way” from meeting Baghdad’s obligation.

“We expected him to show that he would disarm. Yesterday was a disappointing day for those who have longed for peace,” Bush said after White House talks with U.N. Secretary-General Kofi Annan and top Russia and European Union officials on the virtually forgotten Israeli-Palestinian peace process.

In a signal of the intensifying focus on Iraq, the White House also announced that the president will cancel his long-scheduled trip to Africa from Jan. 10-17.

A brief statement issued by the president’s spokesman cited “a combination of domestic and international considerations” and pledged that Bush will reschedule his visit in 2003.

“You have the need to monitor the situation in Iraq,” a White House official said. “We’re entering a new phase.”

The official also conceded that security in Africa, especially Kenya, was a concern.

The growing focus on war was also underscored when Bush met Friday with Defense Secretary Donald H. Rumsfeld and Gen. Tommy Franks, who would lead U.S. forces in any invasion of Iraq, to endorse a proposal to double the U.S. military deployment in the gulf.

Separately, about 30,000 National Guard and military reserve members have been alerted that they could soon be called to active duty, officials said.