MAPUTO, MOZAMBIQUE, NOV. 2 -- Mozambique's legislature unanimously approved a democratic constitution today and cleared the way for multi-party elections next year.

The vote by the 181 deputies present in the assembly ended a 15-year monopoly of power by the ruling Frelimo party, which last year dropped Marxism-Leninism as its official ideology.

President Joaquim Chissano has pledged to hold free presidential and parliamentary elections in 1991, but some diplomatic observers question whether voting will be possible throughout the war-ravaged country.

Rebels of the Mozambique National Resistance, or Renamo, have been waging a 15-year civil war that has cost an estimated 500,000 lives, left nearly 2 million people on the edge of starvation and brought the economy to the brink of collapse.

Renamo has stepped up guerrilla attacks since the legislative debate on the new constitution began last month. Power outages have become common in Maputo, the capital.

The government and Renamo are due to hold a new round of government-initiated peace talks in Rome next week.

Diplomats said the government's change to political pluralism and a free-market economy was largely forced by economic necessity in what is one of the world's poorest countries and by the realization that a highly centralized economic and political structure had not proved workable.

The new 200-clause constitution also guarantees press freedom and independence for the judiciary.

The country's name is changing from the People's Republic of Mozambique to the Republic of Mozambique, while the legislature will become the Assembly of the Republic instead of the People's Assembly.

Chissano announced in July that Frelimo would renounce the monopoly on power it had enjoyed since independence from Portugal in 1974. He has promised elections next year based on one-man, one-vote in secret ballot.

A multi-party system was Renamo's principal remaining demand in peace talks. Chissano has said the rebel movement would be able to register as a political party and compete in elections.