* U.S. keen to see others join counter-terrorism mission
* 12,000 figure at high end of NATO planning estimate
By David Brunnstrom and Adrian Croft
WASHINGTON, June 4 (Reuters) - A NATO-led training mission in Afghanistan next year is likely to total about 12,000 soldiers, including about 8,000 Americans, while some 1,800 Americans will conduct counter-terrorism missions, a senior U.S. military official said on Wednesday.
The United States would also be keen to see participation in the counter-terrorism effort by nations with well-trained special forces, such as Britain or Australia, the official, speaking on condition of anonymity, said.
The 12,000 figure for the NATO training mission given by the official on the sidelines of a meeting of NATO defence ministers in Brussels was at the high end of planning assumptions previously spoken of in NATO corridors.
U.S. President Barack Obama said last week that the United States will cut its force in Afghanistan to 9,800 from the start of next year, split between soldiers who will form part of the NATO training mission and others who will be part of a U.S. mission to combat al Qaeda fighters in Afghanistan.
The United States had not said how many soldiers would be in each mission, "but my assessment is that somewhere on the order of 8,000 will be part of the NATO mission ... and the overall number of 12,000 did include as a planning figure 8,000 U.S. and 4,000 NATO," the official said.
"There are a number of nations that have some very high-end special operations forces that we would welcome as part of that effort," he said.
AL QAEDA FOCUS
Lack of clarity about the counter-terrorism mission until now had hindered detailed discussions on what Britain or Australia might want to contribute, the U.S. official said.
The goal of the mission is to keep up pressure on al Qaeda and its affiliates in Afghanistan to prevent them carrying out attacks in the West.
The United States originally intervened in Afghanistan to deny al Qaeda a sanctuary after the September 11, 2001, attacks.
Both a NATO and U.S. presence in Afghanistan after the end of this year, when NATO-led combat operations are due to end, depend on Afghanistan signing a security agreement with the United States setting a legal basis.
President Hamid Karzai has refused to sign the agreement, but the leading candidates in Afghanistan's presidential race, Abdullah Abdullah and Ashraf Ghani, have both pledged to sign the security agreement as soon as possible, if they are elected in a second round of voting scheduled for June 14.
The plan outlined by Obama foresees a cut in the U.S. troop presence to about half of the 9,800 number by the end of 2015, when U.S. forces will pull back from provincial bases to Kabul and Bagram, the largest U.S. base to the north of the capital.
The U.S. timetable means that NATO's original plan to train the Afghan army from the capital Kabul and four regional bases around Afghanistan is likely to last for just one year.
Kabul will be the focus of the U.S. training effort in 2016.
Germany will lead training of Afghan forces in northern Afghanistan and Italy in the west, but it is unclear whether their regional missions will continue beyond 2015, given the planned U.S. pullback to Kabul and Bagram. (Editing by Ralph Boulton)