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BRASILIA -- Carlos Willian may be only a first-term congressman, but he has already mastered the art of samba-stepping through Brazil's political-party system. Propelled more by personal ambition and parliamentary intrigues than ideology, Mr. Willian has hopped through five parties in just 3? years.

A month after taking office representing the tiny Social Labor Party, Mr. Willian switched to the larger, government-allied Brazilian Socialist Party. Bridling at having to vote with the government, he moved on to the flyspeck Christian Social Party just long enough for a cup of coffee. From there, he joined a populist legislative bloc that tried -- unsuccessfully -- to take control of the large, centrist Party of the Brazilian Democratic Movement. Early this year, Mr. Willian landed in the nationalist Christian Labor Party, which had changed its name and nearly fallen off the map after a candidate it had elected president, Fernando Collor, was impeached in 1992.

Mr. Willian, whose business card doesn't even list his current party affiliation, concedes he has had only one goal while paddling through Brazil's swirling alphabet soup of political factions. "I entered those parties because I did the math on the best way for me to win elections," says the congressman, who is running for a second four-year term in October.

In Brazil, elected officials switch parties faster than Brazilian soap-opera stars switch spouses. Almost 40% of the 513 members of Brazil's 52nd Congress have jumped parties since taking office in 2003, many of them more than once.

Many political scientists say that the rootlessness of elected officials helps to explain why Brazil never seems to fulfill its vast economic potential. President Luiz In¨¢cio Lula da Silva's Workers' Party directly controls just 16% of the seats in the lower house of Congress, and it must horse-trade with nearly a score of other parties with constantly changing rosters to cobble together a legislative majority. As a result, debates over vital reforms drag on for decades while the economy sputters along.

The system also tends to breed corruption. In a scandal that has rocked Brazil for the past year, a congressional commission uncovered voluminous evidence that Workers' Party operatives used a slush fund to pay Congress members for switching into parties loyal to the government, as well as for their votes. Criminal charges have been filed against 40 politicians or their associates.

Brazil is introducing some overhauls aimed at winnowing out smaller parties and limiting switchers' access to committee posts -- though Brazilian politicians are working assiduously to water them down.

Candidates must be registered with a party for at least a year before running on its ticket, but that is about the only legal restriction on switching. Party-hopping is encouraged by Brazil's system of proportional representation, in which the number of congressional seats allotted to each party depends upon its share of the popular vote. The more votes a party's candidates receive, the more seats the party obtains in Congress. Candidates compete within parties to fill the allotment of seats, fostering a divisive system of "internal cannibalism," says congressional analyst Lucio Reiner.

The intense competition within the Democratic Movement party, which has lots of candidates vying for many seats, prompted Mr. Willian to jump to the Christian Labor Party, where he is a big fish in a small party. A radio executive with close ties to Brazil's growing evangelical Christian community, Mr. Willian is counting on his personal appeal with voters to overcome the weakness of his party.

"He's a good man -- whatever party he's in," says Rev. Noedson Dorneles, a minister in Mr. Willian's hometown of Belo Horizonte.

Brazil's system also makes it advantageous for some candidates to alight briefly in parties to ride the coattails of candidates known as "vote pullers." Consider Vanderlei Assis, a doctor who was elected to Congress in 2002 despite receiving only 275 votes. How did he manage that? Mr. Assis ran on the ticket of the biggest congressional vote-getter in Brazilian history, Eneas Carneiro, the standard-bearer of the right-wing Party of the Reconstruction of the National Order. With his gruff demeanor and Coke-bottle glasses well-known to voters after three failed presidential bids, Mr. Carneiro won more than 1.5 million votes in the 2002 congressional race, entitling his party to five seats, besides his own.

Mr. Assis filled one of those seats. Then a year after taking office, he and three other National Order congressmen who recorded modest vote totals left for more mainstream parties. The defectors cited philosophical differences with Mr. Carneiro.

Office holders in several other countries, including Italy and Poland, are known for switching parties frequently. But few can match the moves of Brazil's peripatetic politicians. Take, for instance, Congressman Lino Rossi, who at 10:06 a.m. on Feb. 14 of last year switched to the Party of the Brazilian Democratic Movement from the Progressive Party. But after being publicly assailed by a rival Democratic Movement leader moments after his switch, Mr. Rossi jumped back to the Progressives at 3:47 p.m. that same day.

The champion aisle-jumper of the current Congress, Zequinha Marinho of the Amazonian state of Para, has changed party affiliation seven times since 2003.

Politicians who win elections soon feel a pull toward the larger mainstream parties, which control pork-barrel spending and congressional committee assignments, says Scott Desposato, a political scientist at the University of California at San Diego.

A few years ago, Jurandir Pinheiro, then mayor of the town of Caiabu, explained in coldly rational terms his abandonment of the Liberal Front Party for a party allied to the state governor. "Before being faithful to the party, I have to be faithful to whomever helps me," said the mayor, who was getting funds for roads and housing from the governor.