(Adds comments from news conference, details on new vote)

LA PAZ, Bolivia (AFP)--Bolivia's government and opposition agreed Monday to a vote on a new constitution and early polls next year after left-wing indigenous President Evo Morales vowed to contest just one more reelection.

The accord paves the way for a vote in congress to enshrine the deal and set the dates of Jan. 25 for the plebiscite and sometime in Dec. 2009 for the legislative and presidential elections, officials said.

The ruling Movement Towards Socialism, or MAS, party and the opposition grouping "have reached a decisive accord that completes the structure of the constitutional text," Vice President Alvaro Garcia told a news conference in La Paz.

If passed by Bolivia's 157-seat bicameral congress by the required two-thirds majority, the measures could go some way to resolving political instability in South America's poorest nation, which has repeatedly flared into street violence.

The MAS and its allies hold 84 of the seats, while the opposition has 73.

Tensions remain high after clashes last month between pro- and anti-government demonstrators, which left 19 people dead and led Morales to impose martial law on a northern state.

The government said at the time it feared the volatility could become a civil war.

Today, the country remains divided between the Andean mountains to the west, home to much of the six-million-strong indigenous population backing Morales, and the more prosperous eastern lowlands, where rebel governors are agitating for autonomy.

Morales, a former coca farmer hostile to the U.S. who has allied himself with Venezuelan President Hugo Chavez, had proved a polarizing figure since being elected in 2006.

He has embarked on far-reaching reforms designed to give greater power and wealth to the indigenous population, angering the economic elite in the east, which is mainly of European descent and which refuses to see huge land holdings carved up.

He also has nationalized several key companies in the country, especially in the energy sector, which is Bolivia's main export earner. Most of the natural- gas fields are located in the east.

Several of Morales's reforms are enshrined in the draft constitution.

After the constitutional court declared his decree of calling a referendum in December as invalid (such a decision could only be made by congress), Morales made a characteristically strong-willed effort to get his way.

He walked Monday into La Paz at the head of a march of 50,000 rural and indigenous supporters clamoring for congress to approve the referendum.

The nucleus of the march had set off a week ago from a southern town 200 kilometers (125 miles) away.

The hasty accord between lawmakers as the massive crowd marched toward congress defused what could have been an explosive protest in the capital.

To bring the opposition around, Morales had to agree to not seek reelection in 2014.

He would, however, be able to run in the December 2009 elections, which have been brought forward a year.

Bolivia's constitution only permits one five-year presidential term. But Morales's draft stipulates a two-term limit.

A recall referendum in August showed Morales enjoys the support of more than half the country.