Anti-war protesters should leave US President Bush in "no doubt" about public concern over Iraq, Charles Kennedy has said.
Lib Dem leader will be meeting the president
The Lib Dem leader says he hopes marches to coincide with Mr Bush's visit will be large and peaceful.
He will put people's "anxieties" about the Iraq war to President Bush during a face-to-face meeting.
Mr Kennedy said police should not "overly control" protests, as they seemed to do during a visit to London by the then Chinese president, he told BBC's Today.
Mr Kennedy said: "I think that in a Liberal democracy such as ours, you have every right to make your point... that it can be conducted in a civilised and productive way.
"We should use the opportunity to leave the president in no doubt as to the extent of public concern, not just in our country, but in Europe generally, about the way in which events tragically have unfolded."
But Mr Kennedy stressed: "I hope that we will not see a draconian response of the type which rather disfigured the visit of the President of China at the time, where it seemed to be that legitimate dissent was being overly controlled by security and police forces.
"But we have to recognise that our security and police forces are in a difficult position here and not one of their making."
Mr Kennedy, who joined thousands of people in February's peace protest in the capital, said he would not be joining demonstrations planned to coincide with the president's visit.
But he said he had no problem with other members of his party taking part.
Instead, he will be attending Prime Minister's question time on Wednesday and has the "privilege" of a "one to one" meeting with Mr Bush, he said.
"I will be able to express the anxieties that were expressed by myself, by the Liberal Democrats, by many others who are not Liberal Democrats."
Mr Kennedy said it was "not credible" for the US to pull out a large part of its force by next summer, "as things stand at the moment".
Mr Kennedy said there was "no way" Britain and US troops should "be walking away and leaving a situation of chaos in Iraq".
"Given the rather perilous situation there at the moment, obviously we have an ongoing commitment internationally," he said.
Apart from trying to transfer responsibility for the running of Iraq from the coalition to the Iraqi inbuilt administration, there should be greater involvement from the UN.
Mr Kennedy said he would also be raising with President Bush the case of the Guantanamo Bay detainees.
It would 'be helpful' if a decision is made over detainees
"It would be very helpful indeed if, to coincide with the visit, something substantive was able to be announced which would involve those British citizens being held there either to be returned to this country to face whatever legal processes are agreed upon, or to have a proper legal status confirmed."
Mr Kennedy said it was the duty of responsible British politicians to be raising civil liberty concerns, without being blind to anxieties about "the oppression that terrorism represents".