ASUNCION, Paraguay (AP) _ Center-left independent Carlos Filizzola has been elected mayor of Asuncion, ending a century of rule by two traditional parties in chaotic, first-ever nationwide municipal elections.

The Colorado Party, in power since 1947, maintained control in the majority of interior cities, sharing the vote with the rival Authentic Radical Liberal Party (PLRA), the largest opposition group, according to partial, unofficial results of Sunday balloting.

Irregularities, chiefly involving lack of or late arrival of lists of eligible voters at polling places, were reported by opposition parties.

Throughout Paraguay's 180 years of independence, municipal officials have been named by the president. The Colorados and the Liberal Party, now known as the PLRA, have alternated in power for most of the last century.

Filizzola, a 31-year-old bachelor physician at Asuncion's largest charity hospital, told a victory rally of 35,000 cheering supporters that he would ''sweep corruption out'' of city government.

Organizer of a labor movement among doctors and nurses at the hospital, Filizzola campaigned on a promise to open an office to hear complaints of citizens, improve public transport and attend to the needs of the poor.

An unofficial count of 110,000 of the approximately 255,000 votes cast in Asuncion gave Filizzola 35.2 percent. Runnerup Colorado candidate Juan Manuel Morales received 27.8 percent and the PLRA's Juan Bogado Gondra 20 percent.

Morales and Bogado Gondra both conceded defeat in the race that had matched 12 candidates, seven of them independents who garnered the remaining votes.

Unofficial returns from 123 interior cities and towns gave the Colorados victory in 92, the PLRA in 30 and an independent in one.

Colorado candidates won in Ciudad del Este and Encarnacion, the nation's second and third largest cities. But the PLRA triumphed in Pedro Juan Caballero, the fourth largest, the large Asuncion suburb of Fernando de la Mora and Ypacarai, the Colorado Party's birthplace.

Stunned by the defeat in Asuncion, Morales told supporters he would seek an investigation of ''manipulation of voter lists.''

Under leadership of former President Gen. Alfredo Stroessner, ousted in a Feb. 3, 1989 coup, the Colorados had been accustomed to winning national elections by margins of more than 90 percent. Stroessner, who ruled for nearly 35 years, now lives in exile in neighboring Brazil.

Gen. Andres Rodriguez, leader of the coup, was elected president by a landslide three months later. A Colorado, he instituted democratic reforms, allowing participation by opposition groups previously banned, lifting restrictions on press freedom and redrawing election laws.

Leaders of the PLRA, the socialist Revolutionary Febrerista Party, the Christian Democrats and several leftist groups also complained of frequent absence of election officials and of voting materials, including indelible ink to mark voters' fingers after casting ballots.

Rodriguez acknowledged that the ''historic'' elections were marred by ''a few, understandable imperfections'' caused by ''lack of experience.''