"Democracy is limping along (in Hong Kong)," Lee, founding chair of the Democratic Party in Hong Kong, said after meeting US Secretary of State Condoleezza Rice on Tuesday.
Lee, who is on a trip to Washington where he is due to see White House officials and lawmakers on Capitol Hill, said he had asked the US to put more pressure on Beijing over democracy moves in Hong Kong.
He said Rice, who visited China this month, gave him a "sympathetic" hearing.
State Department spokesman Sean McCormack said the US strongly supports moves towards democracy in Hong Kong.
"The secretary did underline our very strong support for democracy and universal suffrage in Hong Kong," he said.
"The secretary emphasised our conviction that the people of Hong Kong should determine the pace and scope of political reform in accordance with the Basic Law," McCormack added.
Britain ended more than 150 years of colonial rule of Hong Kong on 1 July 1997 and the territory has since been ruled by China under a "one country, two systems" formula.
China governs Hong Hong under a
'one country, two systems' deal
Despite widespread calls for democracy, the Communist leadership in Beijing has been unwilling to let the people of Hong Kong decide for themselves when this should come.
Hong Kong democracy supporters have called for a protest march to demand full democracy on 4 December, raising the possibility of a repeat of a mammoth protest two years ago that rattled the leadership in Beijing.
Lee, a long-time critic of China's policy towarsd Hong Kong, said he had invited Rice to visit the territory and see for herself what was happening there.
Asked whether such a trip might take place even if it angered Beijing, McCormack pointed out that US officials frequently visited Hong Kong.
"In terms of the secretary's travel schedule, we'll keep you updated on that," he said.