Each decade in our lives brings new problems, and the years from 30 to 40 are no exception. That's usually when we begin to realize that our dreams may not come true.

How successfully we negotiate this period, suggests Washington psychologist Robert E. Simmons, may depend on the vigor of our self-esteem.

In our 30s, says Simmons, many of the ego-boosters of extended adolescence come to an end: Easy academic kudos that "made us the apple in the eyes of our parents" cease. Job Promotions, initially rapid, slow down. Our children, we discover, are not Rhodes Scholars.

"By the late 30s," he says, "most people have a fairly accurate sense of how far they will go in their careers."

At the same time, one develops a keener awareness of his or her own mortality as parents grow older and one's body becomes less resilient, wrinkles and bald spots appear and one "loses a step or two on the tennis court."

In short, "It feels in mid-life that the die has been cast and the end has begun to appear on the horizon."

Our 30s, says Simmons, "are underrated as a stressful period. People come to stock-taking, and it can be pretty painful, I think."

Simmons has private practices in Washington and Alexandria, where a large percentage of those he sees are in their 30s. He also serves at the Mount Vernon Center for Community Mental Health, where he will speak on "Narcissism and the Midlife Crisis" at an April 17 conference.

One's self-esteem, says Simmons, grows from infancy primarily through two processes:

We develop a "grandiose self" that is "gradually tempered through childhood and adolescence to healthy ambition, creativity, humor and a healthy need to be stroked by loved ones."

Concurrently, the "association of oneself with an idealized mother" is "slowly transformed into a mature admiration of loved ones, a sense of internal conscience and, perhaps, mature religious feelings."

A parent who praises a child when he does right, but also points out his or her mistakes is aiding in the growth of a healthy or mature self-esteem, says Simmons. The father who comes home drunk and "tells the kid he can't do anything right." may be fostering an immature self-esteem.

Problems in self-esteem may go unchallenged until midlife, believes Simmons, when our dreams are punctured by reality. "The loss of an internal dream" -- writing a novel, becoming president of General Motors -- "that sustains one's self-esteem is as much a loss as the death of a loved one."

Some people, if their self-esteem is based on unrealistic dreams, give up. They count the days until retirement. There can be depression, alcoholism, promiscuity "to deny failing sexual attractiveness and waning potency or fertility." The individual may turn to a "fantastic exercise attempt" to get the body back into its shape at 18.

Those who know their strengths and weaknesses will weather the midlife disappointments more successfully. If they can't attain the company presidency, says Simmons, they may turn to other challenges in their private lives or change careers. "They might just spend more time with the family and enjoy it."

The 30s decade, summarizes Simmons, "can be the worst period of a person's life, or the time during which radical, positive personality changes occur."