PARIS (AP) _ France signaled a dramatic shift in dealings with its former African colonies by ordering French troops in Chad to stand aside while rebels toppled a regime that Paris had backed with guns and money since 1982.

''The time has passed when France could pick and choose the governments in these countries, change them or maintain them as it wished,'' said Foreign Minister Roland Dumas.

Foreign Legionnaires had grandstand seats when Idriss Deby's insurgents marched into Chad's capital, N'Djamena, on Sunday, having chased President Hissene Habre across the Chari river to Cameroon.

In other African capitals, amidst other upheavals in the past, French troops have helped prop up friendly regimes. Habre himself received extensive French military support in countering Libyan incursions in 1986-87. But this time, Habre got no help.

''We didn't aid Idriss Deby. We simply left him alone,'' said the French development minister, Jacques Pelletier.

As recently as June, France helped finance Habre's re-election to the presidency. Billed as Chad's first free elections, only the official party and independent candidates were allowed to run.

But during that same month, President Francois Mitterrand spelled out France's new attitude at a Franco-African summit. He linked French aid to efforts at democratization and stressed that his country's military muscle was not at the disposal of dictators seeking to settle scores with domestic rivals.

Habre was notably hostile to Mitterrand's pronouncements, saying France must not impose Western ideological systems on nations unable to sustain them.

Some skeptics question whether France is prepared to exchange its role of gendarme for spectator in all cases, arguing that expediency dictates the African policies made in Paris.

Jean-Pierre Magnant, a Chad specialist at Bordeaux University's Institute for Political Studies, is among those unconvinced that France will remain faithful to a new policy.

''It doesn't change the foundation of things, it changes the form,'' Magnant said of Mitterrand's pronouncements. ''We support the good dictators, and those that bother us, we let them go.''

France acknowledges that Libya supplied Deby with 40 percent of his arms but, in a departure from past policy, said this was not grounds to contain his advances on Habre.

Some French media have referred to massive Libyan arms shipments, saying Paris conveniently chose to ignore what in the past would have constituted an aggression by a foreign power.

France, which currently has 1,800 troops in Chad, one of the world's poorest nations, had backed Habre after he took power in a 1982 coup d'etat.

Deby, 38, a master tactician trained at France's war college, became Habre's military adviser. But he fled last year amid allegations of a coup, taking refuge in Sudan.

Deby, who began his final offensive Nov. 10, had implored the French to remain neutral and, victory in hand, thanked them.

France has expressed satisfaction with Deby's stated wish for multiparty democracy in Chad. Like most former French colonies in Africa, Chad has had only dictators of various types since gaining independence three decades ago.

Habre has slowly fallen from grace in Paris.

Since the fall of Communist dictatorships in Eastern Europe, several of Africa's strongmen have been forced to move to multiparty systems.

''The shock of 1989 had lots of repercussions in Africa and, especially, Francophone Africa, where bloody dictatorships were everywhere,'' said Magnant. ''It is France which made the one-party regimes.''

Chad is the most dramatic, but not the first, example of recent French neutrality in a conflict in Francophone Africa.

In May, France reinforced its military presence in Gabon, where demonstrations hostile to President Omar Bongo threatened the security of French oil operations. But the French troops, there to protect French citizens, avoided intervening in the violence.

The same scenario was played out recently in Rwanda, where French soldiers helped evacuate foreigners and guard the airport, but engaged in no major fighting against a rebel army.

Besides Chad and Gabon, France maintains troops in the Ivory Coast, Senegal, the Central African Republic and Djibouti, an important French naval base.

The Paris newspaper Liberation said Africa is no longer a top priority for France. With the ongoing changes in Europe and the Persian Gulf crisis, Chad is but a poor man's war, the paper said.

Other African despots must now take note that France is no longer their ''life insurance policy,'' Liberation wrote.