By Stephen Cviic BBC regional analyst

Supporters of Brazil's Workers' Party will be delighted and a little nervous.

Delighted because their candidate, Luis Inacio Lula da Silva (known simply as Lula), has topped the poll in the presidential election - after three previous defeats.

Nervous because he did not win outright and faces a potentially tricky second round at the end of October.

Lula is now expected to win the presidency in the second round

In theory, Lula has little reason to worry.

The third and fourth-placed candidates were both from the centre-left and most of their supporters should opt for Lula in the second round.

But Brazilian voters can be fickle.

In a straight fight between Lula and the government-backed candidate, Jose Serra, Mr Serra will no longer have to watch his back.

He will emphasise his own experience as a government minister and Lula's lack of it - the former trade unionist has never held an executive post.

Mr Serra may also find it easier to capitalise on the more popular aspects of the present Cardoso administration.

Swing to left

But whatever the result, one thing is clear - Brazil's political geography has shifted sharply towards the left.

Throughout the country, left and centre-left candidates have performed well in elections for state governorships and Congress.

President Cardoso governed in coalition with a right wing now in tatters

Whoever eventually wins the presidency will almost certainly be looking to form a centre-left coalition.

The Brazilian right is in tatters.

That is a historic shift because it means that the centrist and leftist parties that together fought against Brazil's military government in the 1970s and 1980s will be united once again.

For the past eight years, President Cardoso, although himself a social democrat, chose to govern in alliance with the right because he felt that only they could provide support for economic reforms.

Now the balance of forces has shifted.

Reasons for success

There are many reasons for the left's success.

It is partly because left-wing candidates are generally seen as less corrupt.

Radical change is demanded by some such as these litter protesters

It is also because they have often shown themselves to be responsible administrators at local level, with more imaginative ideas.

And it shows that the power of the old right-wing political bosses to bring in the votes from the interior of the country is fading.

Although many on the Brazilian left have radical ideas for change, it is unclear just how radical a new centre-left coalition will be.

Neither Lula nor Mr Serra has any desire to antagonise financial markets and risk a debt default.

Both would like to kick-start the economy.

Problems ahead

These two objectives may be incompatible.

If Lula wins, he will be forced to accept tight fiscal discipline for at least his first year in office.

Lula may find his toughest challenges come once he is elected president

He may already be wondering what scraps of radicalism he can throw to his supporters.

Many of them have high expectations which will be disappointed.

There is a fundamental disagreement within Brazil about where the origins of the country's problems lie.

Most supporters of the Workers' Party feel the problem is within capitalism itself.

They believe the country has tried too hard to please financial markets, keeping interest rates high and depressing domestic demand.

They would like more state spending.

Spending plans

But most economists say Brazil's chief economic problem is connected with the role of the state.

They say the state already spends a great deal - on the wrong things.

Even if he wins, Lula may not be able to deliver on all his promises

They want public sector pensions cut and education spending redirected away from universities towards primary and secondary schools.

Only once the public finances are sorted out, they say, can Brazil grow.

Lula may accept some of this analysis. But many of his supporters work in the public sector and would resist such reforms tooth and nail.

Lula - if he wins the presidency - faces some tough choices, as well as the immediate challenge of steering Brazil through rocky financial waters.