CHAR KISHOREGANJ, Bangladesh— When the tide comes in, life pauses on the little silt islands that dot the great river delta of Bangladesh, and for miles around it seems that herds of cattle are standing up to their knees in the Bay of Bengal.
As the ocean rises, pushing a wall of water as high as a man up the riverways ahead of it, the people who make their precarious lives here between the land and the sea retreat, pulling their boats into sheltered creeks.
But when the annual cyclones roar in, in spring and early summer, there is no retreat. Each year, hundreds and sometimes thousands or tens of thousands of people are swept away.
In the floods of 1985, 10,000 to 20,000 people died. The ''great cyclone'' of 1970 killed a half million to a million.
In the endless harsh struggle for land in one of the world's most densely populated nations, the survivors return within days, ''rebuilding their houses,'' as one Bangladeshi put it, ''over the graves of their children.''
On thousands of alluvial islands, known as ''chars,'' the pressure of the world's expanding population is played out in starkest terms as crowding drives millions of people deeper into more perilous portions of the delta, where they battle for survival against nature and one another.
In the competition to cultivate these shifting, inhospitable spits of land, hundreds die each year as they battle each other with knives and clubs for homesteads. A Case Study In Too Many People
One hundred million people live in Bangladesh, an area about the size of Wisconsin, and one-fifth of that area is water, as two great river systems, the Ganges and Brahmaputra, converge to form the largest delta in the world.
If trends continue, the nation's population is expected to reach 160 million by the end of the century, increasing problems already at a crisis level. Experts on the problems of worldwide population growth are studying Bangladesh as an example of what might lie in the future for many nations.
It is agreed throughout the country, and among the char dwellers themselves, that life in the shadow of disaster has bred a race of tough, fierce men and women.
''Their very existence on those shores depends on their being ferocious,'' said Salahuddin Ahmed, whose family migrated to the capital city, Dhaka, from an island area. ''They are closer to nature than we are, and in nature there is no sentimentality.''
Each year, the Ganges and the Brahmaputra, joining in the middle of Bangladesh to form the broad Meghna River, flush what the World Bank has estimated at 2.4 billion tons of silt through the country from as far away as the melting snows of the Himalayas.
As deforestation has brought increased erosion in the Himalayas, the volume of silt flowing through Bangladesh has also risen. Beginning in summer, as the current eases, silt forms uncounted thousands of chars along the rivers and around the ocean's edges. Shifting Landscape: Maps Can't Keep Up
Most of Bangladesh is geologically recent, a gigantic, shifting char formed over the millennia. Rivers slice through the soft land, changing their courses constantly, and little islands appear, disappear and sometimes reappear over the years.
Erosion can eat away as much as a mile of riverbank in a year, and sometimes entire towns are imperiled.
The city of Sirajganj is today fighting off the encroachment of the Brahmaputra River, known in Bangladesh as the Jamuna. The city has already lost its main marketplace, its railroad station and several schools. Yet some maps do not even show it to be on the river's edge.
''There is no such thing as an up-to-date map of Bangladesh,'' a Western relief-agency worker said. ''The rivers and chars are moving about all the time.''
The nation's difficulties have increased since the opening in 1974 of a Ganges River diversion system just across the border in India.
Now, less water flows from India into Bangladesh during times of drought, and more is released during flood season. A reduced current has raised silt deposits and caused flooding upriver.
The shifting landscape of Bangladesh increases the hardships of an impoverished population.
At least 30 percent of the people of Bangladesh - or 30 million people -cannot find paid work or are underemployed, mostly as agricultural laborers. Some 50 percent are considered landless by the Government. And 60 percent are underfed by the minimum standards of the Food and Agriculture Organization of the United Nations. Where Statistics Don't Tell the Story
According to Government projections, this predominantly agricultural nation could become self-sufficient in food grains by the end of the decade. But experts here, both within and outside Government, dismiss this as a largely meaningless statistic.
One reason is the huge difficulties in food distribution in a country fragmented by shifting, often flooded rivers.
A. R. S. Doha, a former foreign minister who left the Government of President H. M. Ershad three years ago, said: ''Almost every day we see Ershad flying about the country in his helicopter. There's not half a dozen helicopters in Bangladesh. He's the one man who can move about the country.''
The other reason that self-sufficiency could be viewed as a mere statistic is the poverty that makes it impossible for most Bangladeshis to afford enough food.
