Asked how he would feel about Britain - the Bush administration's staunchest ally in Iraq - cutting even further in the second half of 2008, Gates would say only that it was too early to assess what troop levels would be required there beyond next summer, when a U.S. troop reduction is to be completed.
The United States has about 165,000 troops in Iraq and plans to pull out at least 21,500 by next July.
Prime Minister Gordon Brown announced Monday that Britain plans to reduce its forces in southern Iraq from about 5,000 to about 2,500 by next spring.
The size of the British force in Iraq peaked at about 46,000 at the start of the war and fell to 18,000 within two months.
Britain's participation in the 2003 U.S.-led invasion - and the continuing presence of troops in the country more than four years later - remains deeply unpopular among the British public. A total of 170 British soldiers have died in Iraq since the March 2003 invasion.
It was Gates' second visit to the British capital since he replaced Donald H. Rumsfeld as Pentagon chief last December. He stopped here to meet Browne in January before traveling to southern Iraq to consult with British commanders on the situation in Basra. At that point there were about 7,000 British troops there.