IN RUGGED CORSICA, SEPARATISTS FEEL LASH OF PARIS

Scores of Sunday drivers took to the coast road south of here to enjoy a warm, brilliantly sunny day. On the Mediterranean beaches, abandoned by the tourists until next summer, parents, children and young lovers picnicked or sauntered along the water. It was all part of the good life that this island of sandy beaches, isolated coves and stony, ruggedly beautiful mountains can offer.

But the seaside calm belied the role Corsica has assumed as one of the most violent issues, and places, in French politics. A series of shootings and bombings by a small separatist group led the Socialist Government of Francois Mitterrand to take a series of tough actions last week, measures that contrasted sharply with the conciliatory stance the Socialists had taken toward this island and its autonomy in their first two years of power. Separatist Group Banned

The Government banned the separatist group, the Corsican National Liberation Front. It replaced several key Corsican police officials with trusted men from France. And it assigned Robert Broussard, an expert in dealing with gangs, to break the separatist group. Mr. Broussard has a reputation as the Kojak of the French police force and is often described in the press as ''supercop'' or ''Zorro.''

The latest events have fueled conservative attacks on the Socialists for having been ''lax'' on law and order questions and for pursuing policies to grant local governments more power. The Socialists' proposals on local government represent a sharp change in the tradition of the French state, which since the time of Napoleon, who was born here, has been one of the world's most centralized regimes. The attacks by the conservatives go to the heart of what the Mitterrand Government hopes to achieve: a socialism that is libertarian in spirit and decentralized in practice.

For many in Corsica, and particularly the non-Corsican ''continental'' French who have settled here, the crackdown was a welcome tonic after the events of recent months. There have been more than 800 bombing and shooting incidents in the last year and the F.L.N.C., as the separatist group is known, has threatened reprisals against continental French who refuse to pay a monthly $450 ''revolutionary tax.'' Corsicans, Too, Are Angered

Last month Dr. Jean-Paul Lefay, a veterinarian, was shot three times after refusing to pay the tax. Dr. Lefay intends to stay in Corsica anyway, but Thierry Cazon, a pharmacist whose business in Petreto-Bicchisano near here was blown up, is ready to leave.