BIRTHS ARE UP and deaths are down, say the computers at the National Center for Health Statistics, offering their first provisional numbers for 1982. You are undoubtedly able to provide your own analysis of the deep philosophical meanings of it all. We shall only say that the trend in both cases is heartening to those of us who expect to be supported, after the turn of the century, by the Social Security taxes then being paid by 1982's new arrivals. From that point of view, the more the merrier.

The peak year for babies in this country was 1957, when 4.3 million of them were born. The figures fell to 3.1 million in 1973, a trough followed shortly by waves of school closings. Now the trend is slowly upward again, to 3.7 million last year. But it's useful to observe that the fertility rate--which means the ratio of births to women of child-bearing age--is rising very little and, if that continues, births won't increase much further. This year's babies are the children of mothers born in the last great surge of population a quarter of a century ago.

But the fertility rate is the least predictable of statistics. In that regard, you might note that marriages are also up, and divorces are down.

In 1982 the infant mortality rate dropped substantially to a new low of 11.2 per 1,000 births. That means it has been cut in half in only 15 years, an extraordinary social achievement. The infant mortality rate is an extremely sensitive indicator, reflecting far more than the quality of medical care. It is influenced by the broadest standards of public health and sanitation, including environmental protection. It's affected not only by the mother's nutrition but by the level of her education. How far down can the infant mortality rate be pushed? No one can say, but it's seven per 1,000 births in Japan.

Among causes of death last year for people of all ages, the cancer rate rose very slightly. But the cardiovascular rate was down significantly. It continues to be true that cardiovascular disease is the major killer among Americans, accounting for nearly half of all deaths. Cancer causes fewer than one-fourth of all deaths.

The result of all these developments is that life expectancy continues to rise. The 1982 figure hasn't been calculated yet. But in 1981 it was 74.1 years, an increase of six months since 1980 and of three years since 1972. It's nice to know, as you go through the years, that the odds are shifting in your favor. The disparity between life expectancies for men and for women continues to be outrageous. In 1981 it was 77.9 years for women, but merely 70.3 years for men. Did you ever see clearer evidence of sex discrimination?