French far-right leader Marine Le Pen said on Saturday U.S. investment bank Goldman Sachs topples governments everywhere and the euro is devastating for her country as she sought to boost her flagging campaign to become president.

Le Pen has slipped in opinion polls ahead of a first-round vote later this month, with one survey showing her in fourth place behind conservative President Nicolas Sarkozy, Socialist front-runner Francois Hollande and hard-left firebrand Jean-Luc Melenchon.

But her loyal support base means Le Pen, the leader of the National Front, can still play a crucial role in the subsequent, two-candidate May 6 runoff that is expected to pit Sarkozy against Hollande.

In a speech that played to populist fears about immigration, unemployment and the power of financial markets, Le Pen painted Goldman Sachs as an all-powerful institution that controlled entire nations as well as the European Central Bank.

Goldman Sachs topples governments everywhere, she told supporters in Lyon, southeast France.

Goldman Sachs places its men at the top of euro zone countries. Goldman Sachs puts its man at the head of the European Central Bank, she went on. In Greece, Italy, the ECB, oligarchs have taken power.

The ECB's current head, Mario Draghi, was a former Goldman Sachs executive before heading the Bank of Italy, while technocrat governments have taken over in Athens and Rome amid the debt crisis.

European ministers, however, have periodically complained about the power of investment banks, and some have said they would like to see them better regulated and blamed them for exacerbating the region's economic crisis.

Le Pen, a 43-year-old former lawyer, also took aim at a favourite target, the euro, which she proposes to dump, calling it a devastating ideology that aimed to bring about a federal Europe.

The National Front is facing pressure from Sarkozy's recent swing to the right. The president has won more far-right support by pledging a crackdown on immigration and threatening to pull France out of Europe's open-borders system.

Last month's murders in the southern city of Toulouse, in which al Qaeda-inspired gunman Mohamed Merah killed three soldiers, a rabbi and three Jewish children before police commandos shot him dead at his apartment building, have also nudged up approval of the law-and-order president.

Sarkozy, trying to win over Le Pen's share of the electorate, told right-wing supporters on Saturday that voting for the National Front would only benefit the Socialists by fragmenting the right.

Polls have shown that most fringe voters will back Hollande rather than Sarkozy in a run-off, with one poll even showing that 16 percent of Le Pen's supporters would switch to the Socialist leader in the second round.

(Reporting by Lionel Laurent; Editing by Alessandra Rizzo)