Normans remember D-Day and the GIs who liberated them.

FRENCHMEN are preparing to welcome some 30,000 of their American liberators back June 6 for the 40th anniversary of the D-Day invasion. They will do this with immense joy, even though D-Day for them was more frightening and sad than liberating. Only afterward did they appreciate the enormity of what they had lived through - and the essential rightness of the affair.

On the morning of June 6, 1944, Michel Hardeley, an engineer, stepped out of an underground shelter and found himself facing an American soldier. With growing fright, Hardeley watched as the soldier reached down toward his trigger, and then farther downward into his pockets, finally to emerge with a pack of cigarettes.

Michel de Vailleville, a young farmer, spotted the Americans from the window of his house. He went to greet them, but before he had taken more than a few steps, the soldiers fired and he was wounded.

Therese Dumont, a grocery store clerk, was too scared to leave the shop's back-room shelter and greet the Americans. Instead, she hid, waiting for her father to return from the countryside. He would never come back: He had been killed.

Ten-year-old Henri-Jean Renaud was also hiding from the tat-tat-tat outside. Peeking through the keyhole, he saw what looked to him like raggedy clowns. But he didn't laugh at the paratroopers with tree branches on their helmuts for camouflage. He was too frightened.

De Vailleville, who spent eight months in a British hospital, is now mayor of St. Marie-du-Mont, behind Utah Beach. He has set up a D-Day museum in his town and will welcome President Reagan to his village.

Renaud will lodge veteran parachutists, now old friends, at his home in Ste. Mere-Eglise. And in her grocery store behind Omaha Beach, Mme. Dumont is stocking up on extra goodies for the returning GIs.

Meanwhile, Michel Hardeley looks out his window to Omaha Beach and the sea below. For the most part, the scene is peaceful today. Hardeley's garden shelter is gone, covered with a bed of roses. The only sounds echoing there now are the lap of the low surf, the crying of sea gulls, and the shouts of children playing.

Hardeley pulls out a book of photos and memories flow forth. A boom woke him up. It didn't scare him: He was accustomed to bombing from Allied B-24s. Still, it shook him enough to make him look out his window. He saw quite a sight, part of the 4,000 boats assembled in history's greatest armada. ''The water was black with boats,'' he recalls. ''It was incredible.''

He scurried to his garden hideout. In the sea below, the water would soon turn red from American blood.

Like other residents Hardeley was looking forward to liberation. The German presence was onerous:

A strict curfew affected everyone. Hardeley had to move out of his beach house. De Vailleville's farm became the site for a German battery; 70 soldiers camped in his fields, the officers in his home. They requisitioned the best food and the little gasoline available.

By spring of 1944, everyone in Normandy was listening to the BBC for news of the invasion. But when the landings came, the Normans were surprised. Most of them equated the Allies with the British, who had been evacuated from this same coast just four years before.

''Everyone was crying Tommy,'' Renaud recalls. ''We knew the Americans were in the war, but we just didn't think they would come here.''

Fright compounded the identification problem. Liberation, like any other episode in war, was scary. Each survivor remembers the screech of bombs and mortars and shelling, the tat-tat-tats of gunfire, the chaos. Then there were the corpses - German, American, and French.

Adding to the tension was distrust between the invading soldiers and the French. The Americans were surprised that civilians had not heeded warnings to flee inland. They feared Germans disguised as civilians and shot anyone who looked suspicious.

For all of these reasons, tragedy struck Mme. Dumont's father and farmer de Vailleville.

But there were small signs of the friendship to come. Hardeley enjoyed his cigarettes - occupied France had little tobacco. At midday, he dodged shells to fetch eggs and bread to share with some Americans.

Renaud recalls, ''The supplies that poured in after the invasion were absolutely incredible. The Germans had nothing. The Americans had everything.''

Villages were overrun with the GIs, who remained through the next winter. Friendships formed. Everyone remembers romances, even marriages, with Americans.

The postwar period brought recovery. Again, the Americans helped, this time with the Marshall Plan.

''You look at the town today, and you can't imagine that there was a war here ,'' Renaud says.

For all this prosperity, the Normans thank the Americans and vow never to forget. Each village has a museum to honor the GIs. Entrance costs are minimal.

''We don't make much money off of the invasion,'' says de Vailleville. ''We feel an obligation to show we haven't forgotten.''

He traveled twice to the United States, gathering documents for his town's memorial. Americans returned the hospitality: While in Washington, de Vailleville stayed with Walter Berry, a 4th Division veteran. Hardeley, Dumont, and Renaud have had similar experiences.

If time has made these Normans fanatically pro-American, it has also mellowed feelings toward the Germans. Under a 1963 friendship treaty, the invasion sites have been twinned with West German cities.