Lebanese vote on June 7 in a poll that pits an alliance including Hizbullah – an Iranian- and Syrian-backed Shiite group that Washington classifies as terrorist – against an anti-Syrian coalition now holding a majority in parliament.
The vice president said the United States was committed to comprehensive peace in the Middle East, including Lebanon.
"I urge those who would think about standing with the spoilers of peace not to miss this opportunity to walk away from the spoilers," Biden added in a veiled reference to Hizbullah, which opposes US-led efforts to forge Arab-Israeli peace.
Biden said he had come to show US support for Lebanon's sovereignty, which "cannot and will not be traded away."
"I do not come here to back any party," he said after talks with President Michel Suleiman, but added that future US aid to Lebanon would depend on the nature of the next government.
"The election of leaders committed to the rule of law and economic reform opens the door to lasting growth and prosperity," Biden declared. "We will evaluate the shape of our assistance program based on the composition of the new government and the policies it advocates."
Hizbullah criticized Biden's visit, which followed one by Secretary of State Hillary Clinton in April, as meddling in Lebanon, and denounced US support for Israel.
"The high American interest in Lebanon raises strong suspicion as to the real reason behind it, especially since it has become a clear and detailed intervention in Lebanese affairs," Hizbullah said in a statement.
Tight vote foreseen
Many analysts predict gains for Hizbullah and its allies, who include Christian leader Michel Aoun, in a tight vote which may lead to the formation of another national unity government.
Saad al-Hariri led a US- and Saudi-backed coalition to victory in the 2005 election, held soon after an outcry over the assassination of his statesman father Rafik Hariri forced Syria to end its 29-year military presence in Lebanon.
Lebanese authorities closed many Beirut streets to ensure security for Biden's one-day visit. Helicopters clattered overhead and police sirens wailed across the capital.
Biden also met Prime Minister Fouad Siniora and Parliament Speaker Nabih Berri, a pro-Syrian ally of Hizbullah. He was due to join Defense Minister Elias al-Murr later for an announcement on US military aid to Lebanon.
Since the 2006 war between Hizbullah and Israel, the United States has expanded military assistance to Lebanon to strengthen its armed forces as a counterweight to Hizbullah, the only Lebanese faction to remain armed after the 1975-1990 civil war.
US military aid to Lebanon since 2006 has exceeded $400 million. Planned deliveries include artillery, tanks and aerial drones as well as light weapons, ammunition and vehicles.
Biden's visit was the first by an American vice president to Lebanon since 1983, the year when Shiite suicide bombers attacked the US embassy and Marine headquarters, and the most senior US visit since that time, a US embassy official said.
Hizbullah, founded to fight Israel's occupation of Lebanon after a 1982 invasion, has since entered domestic politics to secure legitimacy as an armed resistance group, saying its weapons are needed to defend Lebanon from Israel.
Biden, without mentioning Hizbullah, said the United States upheld the principle that "the Lebanese state, accountable to the Lebanese people, is the defender of Lebanese freedom."