RIO DE JANEIRO, Brazil (AP) _ What about the huge foreign debt and corruption scandals? Will the new constitution ever get written? Brazilians will worry later - after Carnival, in the suitable bleakness of Lent.

The world's biggest party officially kicks off Saturday and runs until Ash Wednesday, Feb. 17.

Carnival seems to have been made for Brazilians, and they began working up to it well in advance. So many people had their minds on Carnival this week that it was difficult to transact business with either private companies or the government.

''Carnival is an escape valve,'' said Roberto Couri, president of Rio's Monte Libano Club, a main center of celebration. ''It doesn't matter what troubles there may be. When Carnival comes, Brazilians plunge right in.''

In Brasilia, the normally sedate inland capital, a pre-festival highlight was a ''bar-athon.''

Contestants ran six kilometers, about 3 1/2 miles, and the winner was the person who swilled the most beer from an accompanying tank truck, not the one who finished first.

In Rio, the hub of Carnival, noisy block parties punctured the week and the first balls were held in a series that continues through the celebration.

The dances, which attract thousands of revelers and last all night, range from the sophisticated Champagne Ball to the earthy Bum-Bum Ball.

As insurance against untoward events, the Scala Club, site of several balls, hired a 50-man security squad and installed a 200,000-watt emergency power generator.

One of the most popular events is Rio's ''samba school'' parade, scheduled for Sunday and Monday nights in the ''sambadrome,'' six blocks of open-air concrete bleachers near downtown.

Competing will be the city's 16 best samba schools, which serve as neighborhood social clubs. Among the judging criteria are lyrics, dancing, rhythm, costumes and floats.

As usual, the lyrics will make fun of politicians, failed government policies and corruption in high places.

Each school puts 4,000-6,000 brilliantly costumed people on the route in a spectacle that lasts for about 16 hours each day.

Most participants, dressed as kings, princesses, Amazon chieftains, Greek gods and maharajas, toil the rest of the year at non-descript jobs that often pay the minimum wage of $60 a month.

When it began, the samba school parade was an informal folk event. Now it is big business.

This year the Samba School League, formed in 1985 to protect the clubs' interests, sold exclusive television rights for the parades for a reported $1 million to the commercial network TV Globo.

Samba parade tickets for foreign tourists were jacked up this year to as much as $238 each, payable in U.S. dollars.

Many local travel agents refused to distribute them at such prices.

''It was a holdup,'' said Oscar Dalsenter, president of the Brazilian Travel Agents Association. ''A Brazilian can get a parade ticket for the equivalent of $42, and in cruzados. Why should a tourist pay more just because he is a foreigner?''

The president of the Samba School League, a burly man known only as Captain Guimaraes, said on television: ''In the past, samba schools were exploited, yet they were the ones who created the entire show. Yes, we're after more money ... to protect the traditional values of samba.''

Widespread reports say the Samba School League also raises money through the illegal numbers game and other questionable pursuits, but leaders of the organization deny it.

Because of the new resources, many schools decided this year to exclude ''foreigners'' on a lark, from Brazil and abroad, who paid for costumes and the privilege of dancing in the samba parade.

Elizabeth Nunes, head of the popular Salgueiro School, said the foreigners ''don't know the words to the samba, can't sing and can't dance.''

She said the outside money would be replaced by subsidies from the Samba School League, ''to buy costumes for poor Brazilians who otherwise couldn't be in the parade.''