WASHINGTON – The number of foreign troops in Iraq will drop to fewer than 100,000 by January and most will have left within 18 months, according to that nation’s national security adviser.

“By the end of next year most of the multinational forces will have gone home,” the adviser, Mowaffak al-Rubaie, said yesterday on CNN’s “Late Edition.”

President Bush promised last month to keep American troops, who account for about 133,000 of the 149,000 coalition forces, in Iraq until its government is ready to take over security. The Bush administration is holding a two-day meeting at the presidential retreat in Camp David, Maryland, starting tomorrow to plan ways to prop up the Iraqi government.

Mr. Bush faces domestic pressure over Iraq. An Associated Press-Ipsos poll last week found 59% of adults believe America made a mistake in entering the war three years ago. House Republicans, trying to maintain control of Congress this election year, plan to debate the war this week.

General George Casey, who leads coalition forces in Iraq, was less specific about a drawdown of the American presence, saying on the CBS News program “Face the Nation” that it will depend on how Iraqis manage the transition.

“As long as the Iraqi security forces continue to progress and as long as this national unity government continues to operate that way and move the country forward, I think we’re going to be able to see contained gradual reductions of coalition forces over the coming months and into next year,” he said.

Bush administration officials will meet next week by videoconference with officials of Iraq prime minister Nuri al-Maliki’s government as part of the Camp David gathering. Among the issues will be taming militias and determining what kind of aid Iraq needs for its transition.

The June 7 killing of Abu Musab al-Zarqawi, the leader of Al Qaeda in Iraq, has created an opening for both political and military progress, according to Mr. Rubaie. Zarqawi’s death will encourage other insurgents to join the political process and military intelligence gleaned from the raid has spawned other operations, he said.

“It was very, very useful,” Mr. Rubaie said. “We found a lot of material in that place. We found diaries. We found telephone numbers. We found computers. There was a database.”

On the November 19 killing of civilians by U.S. Marines in Haditha, Mr. Rubaie said, “I will wait for the outcome” of his government’s investigation.

The chairman of the Senate Judiciary Committee, Arlen Specter, a Republican of Pennsylvania, said on “Late Edition” he believed the Armed Services Committee ought to hold hearings into the matter “sooner rather than later.” The chairman, Senator Warner of Virginia, has called for hearings.

Neal Puckett, an attorney for one of the Marines, Staff Sergeant Frank Wuterich, 26, said on “Late Edition” that “it’s just wrong to represent this as a massacre or as something that was unlawful.”