Sheikh Hamad bin Jassem bin Jabr Al Thani, the Qatari foreign minister, said in Doha that the troop pledge was intended to "tell the world that there is an Arab presence, however small, and to say to Israel that we believe in this resolution and that we want to implement it."
He was speaking at a news conference with Kofi Annan, the UN secretary-general, who is on a Middle East tour to push for implementation of Resolution 1701 that went into force on August 14 after 34 days of fighting between Israel and Shia group Hezbollah.
Italian troops will make up the largest single contingent of the UN force known as UNIFIL II.
Annan hoped UNIFIL II would be a "manifestation of international solidarity" with Lebanon. He also urged Israel to lift its siege of the country, saying it was unsustainable.
On Monday, a Qatar airways passenger jet flew to Beirut despite an ongoing Israeli air and sea blockade of Lebanon.
Flight QR 422 arrived with 142 passengers who were greeted by a cheering crowd that gave them roses as they cleared immigration.
One passenger said that many of those on board, including Lebanese, Palestinian and foreign nationals, had flashed victory signs and burst into applause as the jet landed.
The Qatari plane was the first to
land in Beirut following the war
The plane, which was also transporting humanitarian aid, headed back to Doha with 124 passengers on board.
The Qatari foreign minister criticised the blockade and said there was no reason why the flight could not proceed.
"No official blockade of Lebanon has been declared by the United Nations or the international community," al-Thani said.
The Lebanese transport minister, Mohammed Safadi, encouraged other carriers to follow Qatar Airway's example.
"I urge all airlines, whether Arab or other, to force the Israeli air blockade.
A spokesman for Israel's foreign ministry, Mark Regev, said Monday's flight would not have been possible without clearance by Israel.
Israel has kept an air and sea embargo on Lebanon even after the war ended. It says the blockade is to prevent Hezbollah from rearming.
All ships and aircraft require Israeli permission to use Lebanese waters and airspace.