While MTV flashes disjointed scenes of sex and violence to teen-agers across America, their parents soak in the increasingly steamy tub of "Dynasty" and other prime-time soap operas. But even in this genre devoted to passionate adultery and casual fornication, we discover a curious absence: the sexual smorgasbord presented has held little in the way of interracial sex.

Why has television so ignored miscegenation, an important fact of American life and a subject seemingly made to fill TV's insatiable need for the sensational and exploitable?

A decade ago, Norman Lear, iconoclast producer of "All in the Family," spun off "The Jeffersons" and introduced their mixed-race neighbors, Helen and Tom Willis, to American viewers. George Jefferson, Lear's black Archie Bunker in racial attitude, sputtered about the white husband and black wife living upstairs, but the rest of the cast -- in suitably liberal fashion -- ignored the fact of this couple's cross-marriage.

For white liberals like Lear, miscegenation has been the litmus, testing one's color blindness under the most glaring conditions.

For most other Americans, however, miscegenation has been a touchy issue, one not easily confronted despite living in a world where homosexuality (both male and female), adultery in every conceivable combination, teen-age prostitution, pederasty, wife-beating, husband-killing, and -- in both a recent "Miami Vice" episode and the upcoming production of "Tender Is the Night" -- even incest have been given their prime-time airing as family entertainment.

Given the appearance this TV season of several miscegenetic motifs, however, it's possible that the taboo may be weakening.

On "Dynasty," light-skinned actress Diahann Carroll appeared last year as Dominique Devereux, Blake Carrington's illegitimate half-sister, and this year a white lawyer has surfaced as an old lover from a shipboard affair. On "Falcon Crest" this season, Apollonia has been added as a sexual interest for Lance.

TV even is flirting with the other half of the equation. On "Miami Vice," Tubbs got to kiss a white woman. And a "Spenser" episode not long ago ended with Robert Urich's black foil, "Hawk," heading for an assignation with a white woman, with a parting leer to Spenser as he did.

As sociologist Gunnar Myrdal reported in the 1940s, white America traditionally has tolerated a white man's involvement with a black woman, as long as the affair is kept from the public eye and doesn't lead to marriage. But a much stronger taboo has existed against any relationship between a white woman and a black man. Feelings still run high: an Associated Press story in November from Philadelphia reported that Gerald Fox, a black man, and his white wife, Carol, had their new home vandalized when they moved into a predominantly white neighborhood.

The taboo cuts across racial lines. Among blacks, many echo the anger of Afro-American scholar Houston Baker, who said recently of the white heritage traceable on both sides of his family: "It's not a source of pride. It's a source of shame. It's brutal to one's consciousness to think that sexual exploitation was a factor in one's heritage and an accepted one."

And more than a few black women have expressed anger over black men who become successful, then marry white.

As a nation, we are reluctant to discuss racial mixture, and this aversion shows in our language. While black Americans sometimes differentiate, using imagistic language such as "coffee and cream" or "red" to suggest degrees of color, American English as a whole -- alone among languages of mixed-race countries -- lacks a working vocabulary of difference to describe our many shades of color. Our use of "mulatto," for example, is very rare. Only in America does "one drop" of black blood make a person "black," despite Caucasian features and a skin tone lighter than the average lifeguard's.

This national denial of racial mixing, like any fierce repression of reality, has led to fear, and fear has led to greater denial. Where did it begin, this cycle of fear and rage that surrounds interracial sex in America?

Our ideas about miscegenation have a history of their own, with dates and names and landmarks. Ending the cycle of fear depends on confronting this long tradition which has had enormous power over the American psyche -- a power great enough that even today we are shy of talking about it.

From the beginning, when the first African slaves were brought to Virginia in 1619, the colonial leaders had sought, unsuccessfully, to ban racial mixing. A 1630 account tells of a white man, Hugh Davis, who was "soundly whipped" for "defiling his body in lying with a Negro." Virginia enacted the first statute prohibiting intermarriage in 1662, and the other colonies soon followed suit.

These laws, written by white men, banned all intermarriage and punished white women who bore mulatto children. Nonetheless, white indentured servants and black slaves who lived and worked side by side, often loved together as well.

By the time that the 13 colonies became the United States, more than 60,000 people of mixed black and white ancestry already lived in the new country.

After the American Revolution, many slaves were freed in the spirit of the time. But the increased number of freed mulattoes created the need to define who was a free white citizen and who was not.

In 1785, for example, Virginia passed its first such law, defining as black anyone with a black parent or grandparent. Anyone with less than one-fourth black ancestry was legally white. When ancestry was unknown, a jury inspected the individual in question and decided according to appearance, often in favor of light-skinned mulattoes who wished to be classified white.

Pre-Civil War court and legislative records in Virginia, examined by historian James Hugo Johnston, reveal a brisk business in miscegenation: Courts fined white women for having mulatto children and ministers for marrying mixed couples; white slave owners manumitted their mulatto sons and daughters; white women petitioned for divorce because their husbands cared more for slave mistresses, and white husbands petitioned for divorce because their wives were involved with black lovers.

Although intermarriage and other liaisons between white women and black men were more common in the pre-war South than generally believed, by far the greatest incidence of miscegenation took place between white men, owners and overseers, and black female slaves, who were subject to what historian Eugene D. Genovese calls "a cross between rape and seduction."

In her pre-Civil War "A Diary from Dixie," Mary Boykin Chesnut, of Charleston, wrote: "God forgive us, but ours is a monstrous system, a wrong and iniquity. Like the patriarchs of old, our men live all in one house with their wives and concubines; and the mulatto children one sees in every family partly resemble the white children. Any lady is ready to tell you who is the father of all the mulatto children in everybody's household but her own. Those, she seems to think, drop from the clouds."

Thus for most of its history, American slavery bred interracial sex as a commonplace, and for free men and women of color it was possible to move from black to white in three generations. In short, there was no absolute divide between the races.

The changes that began about 1830 resulted from a number of causes. Most important was the rise of King Cotton, creating vast new plantations where slavery was an economic necessity. Cut off from importing new slaves by an 1807 law, the South turned to the domestic supply. Laws were changed to prevent the freeing of any slaves and to insure that mulattoes were considered black and thus subject to enslavement and sale.

In addition, when the abolitionist movement blossomed in the 1830s, the attack centered on slavery as a moral evil rather than as a problematic legal or economic institution. Slavery was portrayed as a sin committed by each individual slave owner. Under such moral attack, slavery apologists had to find a moral justification, which they did in the doctrine of black inferiority and white paternalism.

Beginning with Dr. Samuel George Morton's "Crania Americana" (1839) a string of "scientific" arguments appeared suggesting how and why the inferiority of blacks came to be.

In the 1850s, Thomas Drew proposed that blacks were inherently "savage" and needed slavery to domesticate them. Of course, as soon as slavery's restraints were removed, the "happy darky" would revert to savage monster.

In 1860, a Louisiana physician named Samuel Cartwright argued that blacks were some of the animals created before Adam and Eve, over which Adam was given dominion.

Jefferson Davis held a similar view, and slavery apologist W. W. Wright contended that the strongly felt prejudice against color was actually a natural aversion to hybridizing, thus giving white anti-amalgamation sentiment a "scientific" ground.

Mulattoes, of course, posed a serious problem because they blurred the distinction between races. When the increasing "whiteness" of slavery after 1830 could no longer be ignored, it was dealt with by introducing the "one-drop rule." The evolution of the one-drop rule in the decades between 1850 and 1915 transformed race relations in this country.

Following the Civil War, Southern states under Reconstruction governments revoked laws against intermarriage, beginning with Louisiana and Mississippi in 1870. There was a flurry of mixed marriages, especially between white women and black men, one reason being that the war had left relatively few white men of marriageable age.

After Reconstruction, when white Democrats regained political control of state governments, a new round of anti-miscegenation laws followed the colonial pattern, banning all intermarriage and any relationship between black men and white women, while ignoring extramarital relationships between white men and black women.

But these new laws also incorporated the "one-drop rule," and most lasted on the books of Southern states until desegregation and the Civil Rights movement of the 1960s. One of these laws, that defined as "black" for purposes of preventing cross marriages anyone with 1/32 Negro heritage, was still in place in Louisiana until 1983.

Another thing that changed after the war was the white male attitude toward black males. According to Genovese, "the violence-provoking theory of the super potency of that black super-penis . . . did not become an obsession until after emancipation, when it served the purposes of racial segregationists."

The growing myth of the black man as a genetic sexual monster fanned the Negrophobia of the 1890s, a myth encouraged by popular novelists such as Thomas Nelson Page and later trumpeted by Thomas Dixon, Jr., author of "The Clansman." With D. W. Griffith, Dixon later coproduced "Birth of a Nation," the film based on his book.

Social historian George Frederickson argues that depicting black males as rapacious beasts justified the lynchings that occurred more and more frequently after Reconstruction.

During the 1880s and '90s, the concept of an exploitable underclass made up of blacks and immigrants was bolstered by capitalist support for theories of social Darwinism. Common belief held that mulattoes -- the word comes from the Spanish for "mule" -- were genetically weakened hybrids that would sink into sterility and cease to exist within a generation or two; blacks generally would be eliminated before too long in the battle for survival of the fittest.

Even some blacks came to believe these arguments and feared that miscegenation would weaken their race.

During the same period, roughly 1880-1900, the North abandoned its interest in the welfare of blacks. Its strong feelings against slavery had always been accompanied by equally strong feelings against miscegenation and in favor of colonizing blacks in Africa, once they were free. At the Civil War's end, for instance, only Massachusetts allowed blacks their basic rights.

This increasing loss of support developed from the great increase in industrialization following the war, which gave rise to a middle-class fear in Northern cities of economic competition with, and loss of political power to, immigrants. The situation provoked much Northern prejudice toward Irish, Italians, Slavs, and other ethnic groups. The Northern middle-class began to look with new understanding on the Southern attitude toward blacks.

Among whites, turn-of-the century beliefs that blacks were lower on the evolutionary scale, with hereditary disposition to disease, led inevitably to rabid fear of interracial sex. Among blacks, fear that miscegenation would mean the end of their racial identity and horror at the state-supported terrorism of lynchings achieved the same result.

The complex web of segregation rules that followed were primarily designed to keep black men away from white women, whom intellectual historian W. J. Cash called "the perpetuators of white superiority in legitimate line."

Only by introducing a mulatto child through a white mother would be the "purity" of the white race be threatened; racial purity would not be "polluted" by a white man's fathering a mulatto child who would follow the mother's caste and be "black."

Given the absolute division between black and white, under the "one-drop rule" mulattoes were forced into the black world and, by the turn of the century, "passing" became an important issue. Because of the strong social bonds of family, friendship, and sensibility, relatively few light mulattoes attempted to pass for white, but the worse segregation became, the greater the benefit to one who chose to do so.

The threat posed by passing created a white Southern obsession with racial purity, manifested in excruciating concern for family genealogies.

In 1915, 90 percent of all blacks still lived in the rural South, blacks and mulattoes were isolated from the white world, and their combined gene pool was 20 percent white.

According to studies by historian Joel Williamson, from this point on no statistically significant miscegenation took place between blacks and whites; the white genes were diffused through the intermarriage of blacks and mulattoes, creating what he calls a "new people" of "brown America."

By this date, the young blacks and whites coming of age were the first generation to have lived all their lives in a rigidly segregated society that insisted on the one-drop rule. Both blacks and whites accepted this rule, and both cultures were strongly opposed to miscegenation.

The acceptance of the one-drop rule was so universal that the 1920 census was the last to count mulattoes; after that all mulattoes were classified as "Negro," officially creating a simplified, biracial America.

When World War I cut off the supply of immigrants to Northern industrial cities, a great migration of black Americans -- some estimate as high as 2 million in four years -- ventured from the rural South to the urban North.

The system of segregation that greeted them was more de facto than de jure but none the less successful in maintaining the separation of black and white cultures. Despite the brief flirtation by white sophisticates with black culture during the Harlem Renaissance, the two worlds remained apart, and miscegnation remained the great taboo.

While miscegenation takes many forms, from marriage to casual sex, from rape to prostitution, little data is available except on marriages. Since World War I, cross marriages in this country have remained at less than 1 percent of the total.

Interestingly, however, white women have married black men much more frequently than white men married black women. A study of mixed marriages in Philadelphia between 1922 and 1947, for example, showed that white women cross-married more; in one sample of 50 mixed marriages, 44 were by white women.

More recently, the civil rights movement stimulated a 63 percent increase in cross marriages during the 1960s, due almost entirely to white women marrying black men; the number of white men marrying black women actually declined during the same period.

From 1970 to 1980, according to the Bureau of the Census, the number of black-white marriages increased from 65,000 to 167,000; about three quarters of them had black husbands.

The real effect of the '60s, however, is just now being felt. During that decade, the civil rights movement, with the accompanying legislation and court actions, sounded the end of rigid social segregation.

As a result of school integration and busing, for example, millions of American children, black and white, North and South, have grown up together over the past 20 years.

Obviously, schools and jobs and neighborhoods still discriminate and segregate.

But something has changed. No longer do black and white Americans, particularly American youth, live in two isolated cultures, knowing nothing of each other's social lives, values, music, dress, work.

In a recent segment of TV's "Kate and Allie," the character Kate, played by Susan St. James, dated a black man twice. The script made the point that while the adult characters found the situation strained and difficult, their children found it "cool."

The black and white youngsters coming of age today are the first generation of Americans since the 1890s to be raised in steady social contact with each other, just as the generation that came of age in 1915 was the first to grow up under total segregation and the one-drop rule.

Many divisions remain between black and white in this country but, for the first time in almost 100 years, the great gulf of social mystery no longer yawns so very deep or so very wide.

By 1915, miscegenation to any socially significant degree had ended in the United States. In the mid-1980s we may be witnessing hints of some possible renewal. Now that television, the great common denominator of popular culture, finds miscegenation acceptable at long last, it may be telling us something.