Diana Bassick and Raymond de Profit lived together as man and wife for 24 years, raising five children into what the neighbors thought was a happy white family.

But South Africa's race classification laws have ended those good times.

The pair's 20-year-old son, Graham, committed suicide because he could not marry his pregnant girl friend. In the investigation of his death, police found that Diana and Raymond had been faking their marriage all those years. Now they want to make it legal, but can not.

The problem: Diana, whose mother was white, but who never knew her father and was raised by a colored family, is classified colored, or racially mixed. Raymond, son of a Belgian father and British mother, is classified white.

Since the children were born out of wedlock, they were registered under Diana's name and also classified colored. Graham's girl friend, Sonya, was the daughter of Afrikaners - and therefore classified white and out of reach.

After a fight with his mother over what to do about it, Graham stormed out of the house four years ago and walked in front of a commuter train. A government inquest ruled it was suicide caused by despair over Sonya.

"He would not have killed himself if it wasn't for these laws," said Diana in an interview at her working-class home in Cape Town. "It's four years ago, but I still expect to see him come through the front door."

In South Africa, such a cross-racial marriage is forbidden by law, even though her wavy black hair and lightly tanned complexion give Diana the appearance of someone who might have come from a southern Mediterranean country like Greece.

For Graham, as for everyone born in South Africa, the crucial information on his birth certificate was the entry after "race." That word - colored - was the key to what jobs he could hold, how much he was paid, what school he could go to, where he could live, with whom he could have sexual intercourse, whom he could marry, how large his old age pension would be, in what hospital he could be admitted and even the cemetery in which he could be buried.

The Population Registration Act, which requires every citizen to be classified into a race group, belongs to a package of legislation that the ruling National Party enacted in the early 1950s to help carry out its policy of apartheid, or racial separation.

The package also includes the Immorality Act, which bars interracial sex: the Mixed Marriages Act, which forbids interracial marriage, and the Group Areas Act, which outlaws integrated neighborhoods.

When the government started classifying, many disputed their racial label and hired lawyers to wade through the paperwork and argue their cases before a court that handled appeals used to be heard every year.Now, only a few cases remain.

Requests for reclassification first go to the Department of the Interior, which never informs the person seeking a new category of the reasons for its decision. Last year, government figures show, 115 applicants won reclassification out of a total the government refuses to reveal. Change in classification can mean a whole new life style. Whites and colored carry "books of life" as identification. Blacks carry "reference" books, known as "pass" books because inside must be a valid pass giving the holder permission to live or work in a specific city.

"Getting reclassified is like murder," said one colored woman. "You live in a certain neighborhood, have certain friends and a family. And when you change, you go to a new neighborhood, you don't see your old friends and many people for their children's sake, stop coming to visit their families."

Roma Sabatini, a white-classified store cashier in Johannesburg, is trying to switch to colored because, at 22 after growing up with her colored mother in a colored neighborhood, she wants to marry her colored boy friend.

"This business of being white is hanging over me like a cloud," said Roma, who resembles many colored people. I sent a letter to the Classification Bureau three years ago, saying I want to be reclassified colored. It's not the way they want to classify me; it's the way I feel. I go to colored places, I go out with colored men. My heart is feeling colored and my mind is saying colored. I don't want to leave the country to get married."

The Department of the Interior agreed to reclassify Diana Bassick's remaining four children white following Graham's suicide and turned a blind eye to her cohabiation with De Profit. With her secret now known, however, Diana also applied for reclassification so she could marry Raymond legally.

Her request was denied. As usual, no reason was given. But Diana's lawyer was told that the fact she was still of childbearing age had been a factor in the refusal. So after a hysterectomy in 1975, Diana applied again.

The answer was a in a note from the Interior Department secretary to her lawyer this spring: "I do not see my way clear to amend her classification."

"It's so late in my life," said Diana, now 51. The only thing I look forward to in my life is to belong to someone. I know we are already happy, but one does want to make it legal. I want to marry the father of my five children."

In the original classifications, racial appearance and general acceptance by others were the prime factors. In dispute, besides his appearances, a dissatisfied South African could present affidavits from neighbors saying they always thought the person was colored, or white, or black, and was accepted as such by the community.

Decisions used to be arbitrary and often reflected the attitudes of those who made them. Some racall stories of borderline cases being decided by the "pencil test" - if a pencil stuck in someone's hair, he was black, not colored.

But a 1966 amendment to the Population Registration Act made descent the chief criterion instead of appearance and acceptance. Today, these factors come into play only if family descent is unclear.

This affected colored families most, since many were borderline cases under the old criteria. Whole families among the country's 2.4 million coloreds have been split down the middle by fair-complected members who moved into the white category.