Rice told reporters as she flew into Beirut from Saudi Arabia on Thursday the purpose of her visit was to support the Lebanese government.
"The sole purpose of the trip is to express support for the Lebanese people and the Lebanese government as they continue to try to recover fully their sovereignty," she said.
She later said after talks with Fuad Siniora, the Lebanese prime minister, that it was "time to reiterate and to affirm the firm support of the United States of America for the Lebanese people".
Rice's visit came as political tension was rising in Lebanon where the majority anti-Syrian coalition has launched a campaign to unseat Emile Lahoud, the Lebanese president and a close ally to Damascus.
In a snub, Rice avoided meeting Lahoud and suggested he should resign because of his links to the past when as recently as a year ago Lebanon was effectively run from Damascus.
"They need a presidency that looks forward not back and that defends Lebanese sovereignty but it is a decision that they will have to make," Rice said.
"The sole purpose of the trip is to express support for the Lebanese people and the Lebanese government as they continue to try to recover fully their sovereignty"
US secretary of state
Due to security fears in a country where several anti-Syrian figures have been killed in recent months, Rice did not announce her trip before leaving earlier on Thursday from Saudi Arabia.
During her four-hour visit she met officials and politicians who are trying to establish Lebanon's independence from Syria which, until last year, had thousands of troops based in its tiny neighbour.
Rice reiterated Washington's call for disarming anti-Israel Hizb Allah fighters in line with UN Security Council Resolution 1559, but indicated there was no deadline for the government to do so.
"This is part of an evolutionary process that is going on in Lebanon and we have tried to be supportive of that process that the Lebanese themselves are carrying out," she said. "But there is no doubt that 1559 is going to have to be implemented."
Siniora, in apparent reference to the time the Bush administration has given him to tackle Hizb Allah, said: "Really, I appreciate as well the show of patience that Secretary Rice has been showing to Lebanon."
Rice also said Syria needed to cooperate fully with a UN investigation into the killing just over a year ago of Rafiq al-Hariri, a former prime minister, which many people blame on Damascus.
Rice held talks with top anti-Syrian politicians Walid Jumblatt and Saad al-Hariri, son of the slain ex-prime minister. She also met Maronite Christian cleric, Cardinal Nasrallah Sfeir.
Rice, who initially said she would only speak on the phone with Nabih Berri, parliament speaker, another close ally to Damascus, later changed her plans and paid him a brief visit.