At least 1 million people marched here today in a stridently anti-American demonstration past the boarded-up U.S. Interests Section, where nearly 400 Cubans have taken refuge in hope of leaving the island.

The marchers carried placards with caricatures of President Carter, calling him the "godfather of delinquents, vagrants and worms" who take advantage of President Fidel Castro's offer to let those who want to leave get on boats to Florida.

From the outside, the U.S. mission looked like an abandoned building. The Cubans and about 10 U.S. diplomats and Marine guards inside sat quietly eating box lunches provided by Western embassies, litening to the chants from the street and watching the demonstration live on Cuban television.

The demonstration originally was scheduled last month to protest a planned U.S. naval exercise at Guantanamo Naval Base in eastern Cuba. Since Carter canceled the exercise, preparatory propaganda for the march and today's chants and placards focused more generally both on the departures and Cuban demands that the United States abandon Guantanamo, lift the economic embargo against Cuba and cease surveillance overflights reinstituted by Carter this year.

Perhaps more important that those issues in the eyes of the government, the march clearly was designed to reawaken mass emotions against the United States as revolutionary Cuba's number one enemy.

Not since the early 1960s, when soured relations between the two contries provided Fidel Castro with his principal instrument of domestic cohesion, has anti-American sentiment been whipped to such a fever pitch.

Cuba has refused to negotiate the fate of those inside the U.S. mission and has announced its intention to ignore a White House ban on Cuban refugee arriving illegally in the United States by boats.

But the Carter administration apparently believes the Cuban intransigence in part was motivated by the buildup for today's demonstration. There are hopes, in words of one informed source, that "after this we can get down to something substantial" in terms of talks with the Castro government.

The march was highly organized by zones within the capital and the surrounding province. Similar preparations an demonstrations took place in each of the country's 14 provinces.

In Havana, neighborhood groups arrived at a central staging area half a mile from the interests section, in staggered busloads throughout the day.

Beginning with several hundred representatives from peasant cooperatives on horseback, the demonstrators in ranks stretching across the six lanes of the seafront boulevard walked past the U.S. building and continued another half mile to buses waiting to take them home.

Although participation in the event was not obligatory, and the majority of the demonstrators -- who appeared to be at least half of Havana's 2 million population -- seemed genuinely enthusiastic, its organization by neighborhood zones ensure that most people would participate.

Much of the regimentation in Cuba stems from strong peer pressure and the fact that decisions on allocation of scarce consumer goods and upward mobility frequently depend on the level of one'c activity in "revolutionary tasks."

Most of the marchers either talked among themselves or sang revolutionary songs until they came within a block of the seven-story U.S. mission -- a 1950s-style building that stands alone along the waterfront and served as the U.S. Embassy until relations were broken in 1961.

Sometimes led by cheerleaders, the groups then began to chant slogans -- "Carter and the CIA belong in the same pigsty," "Cuba will never surrender," Fidel, be tough with the Yankees."

The government appeared to have gone to great lengths to avoid violence -- either from the demonstrators or outside provocation.

Both sides of the boulevard along the entire march route were lined with armband-wearing Cubans appointed by their neighborhood or workplace committees. Surrounding the mission itself, several thousand civilian militiamen formed a human wall several layers thick. Cuban Army troops were stationed along the streets behind the mission leading to the main downtown area.

Offshore, naval patrol boats -- some with what appeared to be frogmen in wetsuits -- and military helicopters passed back and forth.

Those inside the mission were on strict oders not to look outside from any point where they could be seen by the demonstrators. At one point, however, a man emerged from a door on the seventh floor to walk briefly along an outside balcony. The marchers stopped dead and then began jeering at him.

Near the end of the march route, where most of the demonstrators had stopped chanting and begun chatting, their attention was solicited by a small group of Cubans standing outside a house marked as the home of "worms," meaning those who have applied to leave in the boatlift.

Several windows were broken and walls were painted with signs. The people standing in front of the house led each group of passing marchers in shouting denunciations at the family inside.

For the most part, however, except when the demonstrators were directly in front of the U.S. mission, the marchers seemed more in a holiday than a hostile mood. Although many carried the caricature posters and scarecrow figures of Carter that were reminiscent of anti-american demonstrations in Iran, smiles were more often in evidence than angry glares.

Numerous groups brought their own conga drums and danced along to a salsa beat.

Several blocks from the U.S. mission, on downtown Havana's main street where the stores were closed for the march, lovers and families who had finished the march strolled or took to the grass of adjoining parks.

Lines formed at a truck selling packaged half gallons of ice cream, an unusual item in a country where grocery stores normally carry only essentials and rationed goods.