The winding down of the singles scene: an NBC report

Has the curtain finally come down on the ''swinging singles'' scene? The answer is a resounding ''Yes!'' if you believe NBC reporter Jack Reynolds , who hosts a disco-beat ''NBC News Report'': Second Thoughts on Being Single (Wednesday, April 25, 10-11 p.m.). On this program, awhole series of ''born-again prudes'' (as one women calls herself) testify that the ''baby boom'' generation has become more conservative in its sexual behavior.

Says reporter Reynolds in his hour-long, determined effort to prove his theory: ''Many of the generation which flaunted the singles life style are now questioning the cost in loneliness.''

Now, ''Second Thoughts'' may be completely accurate in its conclusions about this change, and about how persuasive certain factors were in effecting it - such as sexually transmitted diseases and the running out of the biological clock of motherhood for ''liberated'' women. But by carefully selecting for interview only those who concur in his thesis, Reynolds weakens his documentary.

In most cases, those who appear are the ones who seem eager to present a new attitudetoward their own past behavior, saying it had all been a mistake. And the experts seem to be most interested in promoting their own expertise. A few interviews with women and men who disagreed would have strengthened the show considerably. And the impact on today's single population of such factors as homosexuality, single parenthood, etc., is not considered.

The program is filled with snappy sloganeering, one-sided research, and pseudo-scientific reasoning. Among the statements that seem dubiously researched - although some may be accurate:

''According to the evidence, most women begin thinking about that lifetime partner sooner and more fervently than most men do.''

''The sexual revolution has reduced male-female intimacy to the moral equivalent of fast food. Women are finding that junk sex is no more satisfying than junk food.''

''In 1980 only 11 percent of the new households established in America were composed of married couples. However, by 1983, about 71 percent of all our new households consisted of a husband and a wife.''

Mr. Reynolds arrives at a conclusion bound to be widely acclaimed because it verbalizes the hopeful thinking of so many moralists among us: ''We're witnessing one of those pendulum swings that periodically occurs on the American scene; this time it's a swing toward marriage and away from casual sex. . . .

''The great American disease of this century is loneliness. And the baby-boom generation is rediscovering that a good marriage is one of the best cures.''

''Second Thoughts on Being Single'' is a swinging documentary - but like too many of the habitues of those swinging-singles bars it seems to condemn, the documentary may very well have been taken in too easily by glib talk.