An aggressive and good-humored President Francois Mitterrand, obviously in a confident mood, was the overwhelming favorite to lead a field of nine candidates Sunday in the first round of the French presidential election.

Premier Jacques Chirac, a right-wing Gaullist candidate, was expected to take second place easily and thus win the right to face Mitterrand in a runoff for the presidency May 8.Under French law, the two top candidates meet in a second and final round if no one receives more than 50 percent of the votes in the first round. No one, not even the late Gen. Charles de Gaulle, has won in the first round since popular elections of presidents began in 1965.

A number of potential campaign issues the possible release of French hostages in Beirut, the slaying of three French police officers by separatists in New Caledonia, a debate over a television debate surfaced on the eve of the first round of voting, but none were expected to influence in any significant way the choices of the more than 38 million eligible voters in Sunday's first round. The issues, however, could take on importance during the next two weeks of the runoff campaign.

No polls are allowed to be published in France during the week of an election. In the last poll published by the Paris newspaper Liberation a week ago, the 71-year-old Mitterrand, a Socialist, received 38 percent of the sample polled, followed by the 55-year-old Chirac, candidate of the Rally for the Republic party, with 23.5 percent and the 64-year-old Raymond Barre, a former premier and candidate of the center-right Union for the French Democracy, with 19 percent.

A few months ago, Barre was a heavy favorite to join Mitterrand in the runoff, but his lackluster campaign faltered and fizzled in the last few weeks. Barre, unaggressive, professorial and often boring, never tried hard to explain to conservative voters why they should vote for him rather than Chirac.

The main candidates, according to the poll, were followed by extreme rightist Jean-Marie Le Pen with 9.5 percent, Communist Party candidate Andre Lajoinie with 5 percent, Pierre Juquin, a breakaway Communist, with 2.5 percent, environmentalist Antoine Waechter with 2 percent and Trotskyite Arlette Laguiller with 0.5 percent. Extreme leftist Pierre Boussel polled nothing.

Although the total number of rightist votes outnumbered leftist votes, the poll also showed that enough Barre and Le Pen voters would scorn Chirac to ensure a Mitterrand victory in the runoff by 54 percent to 46 percent.

Speaking for two hours in informal tones at his final rally, Mitterrand accused Chirac of continually coming up with new conditions for a televised debate between the two during the second round.