Officials in the capital Sanaa confirmed the government had accepted the plan drawn up by Gulf Arab states.
Mr Saleh will hand power to his vice-president one month after an agreement is signed with the opposition, in return for immunity from prosecution.
At least 120 people have died during two months of protests.
The US has welcomed the announcement; a statement from the White House urged all parties to "swiftly" implement a peaceful transfer of power.
Opposition leader Yassin Noman was quoted by Reuters news agency as saying he welcomed news of the handover but would not take part in a proposed national unity government.
The opposition have been insisting they will not accept immunity from prosecution for Mr Saleh and his family.
If Mr Saleh steps down as expected, he will join Tunisia's Zine al-Abidine Ben Ali and Egypt's Hosni Mubarak as the latest Arab leader to lose power because of a popular revolt this year.Strike action Continue reading the main story Lina Sinjab BBC News, Sanaa
The opposition say they welcome the initiative but seem reluctant to serve in a government with the ruling party. Opposition members have also been sceptical about any deal which would see President Saleh transfer power but not leave office immediately.
The timing of the announcement by the president is surprising. Earlier in the day, he delivered a tough speech to members of the country's army in which he accused the opposition of dragging Yemen into a civil war.
But on Friday Yemen saw some of the largest demonstrations so far as hundreds of thousands took to the streets in rival protests in support of both the opposition and the president. And on Saturday, opposition activists called for a general strike in the country.Tariq Shami, a spokesman for Yemen's ruling party, told Reuters the party had informed the Gulf Cooperation Council "of their acceptance of the Gulf initiative in full".
Under the plan proposed by Saudi Arabia and five other statesWithin a month of signing an agreement with the opposition, Mr Saleh quits and hands over to his Vice-President, Abdu Rabu Manur Hadi Mr Saleh appoints an opposition leader to run an interim government tasked with preparing for presidential elections two months laterMr Saleh, his family and his aides are given immunity from prosecution
Washington has urged Mr Saleh to set about the transition immediately.
"The timing and form of this transition should be identified through dialogue," state department spokesman Mark Toner said.
Hundreds of thousands of people attended a rally in support of Mr Saleh in Sanaa on Friday but comparable numbers turned out for demonstrations against him in both the capital and the southern city of Taiz.
On Saturday, a general strike called by the opposition caused disruption in Taiz, the port city of Aden and other towns, although apparently it had little effect in the capital.'Loop-holes' Continue reading the main story President Ali Abdullah Saleh in power since 1978Population 24.3m; land area 536,869 sq kmThe population has a median age of 17.9, and a literacy rate of 61%Youth unemployment is 15%Gross national income per head was $1,060 (£655) in 2009 (World Bank)Yemen is the Arab world's most impoverished nation and, even before the current protests, it was becoming increasingly chaotic, with both al-Qaeda and separatist challenges to the government's authority.
Mr Saleh suffered a major political reversal last month when a slew of ministers and ambassadors resigned in protest at the shooting of 45 people at a demonstration in Sanaa.
The president promised earlier not to renew his presidency in 2013 or hand over to his son. He has made - and broken - similar promises in the past.
Members of the opposition coalition say they are wary of loopholes that could keep Mr Saleh, a canny politician, in office.
One opposition leader told Reuters that ending the protests would be a major sticking point.
The opposition, the unnamed leader added, did not fully control the hundreds of thousands of people, many of them youth activists, who have taken to the streets.
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