No problems can quite compare with those Problems That Nobody Wants to Talk About. Correspondent Bill Moyers and executive producer Howard Stringer's unit at CBS News take on just such a problem tonight, and they do it with such diligence and decency that though their report is hardly painless viewing, it is also facinating and essential.

"CBS Reports: Anyplace But Here." at 8 on Channel 9, excamines the new dilemma facing the mentally ill in America and the people who try to help them. The old impersonal institution is in disfavor and the numbers of hospitalized mental patients has fallen considerably. Now the goal is to get the mentally ill back into the mainstream and out of debilitating isolation.

Clearly, there are as many complications to this as a human mind, healthy or sick, could possibly imagine, and one of the most obvious lies in the fact that in may cases, the mainstream rejects or ignores the expatriates attempting to return.

At first, "Anyplace But Here" seems almost cruel in its invasion of privacies. Moyers and a camera crew were allowed into the Creedmoor Psychiatric Center in New York State and there talked to patents, relatives of patients, and staff members. Some of the patients appear separated from "normal" society only by a shadow of difference-and by the walls of Creedmoor.

Some sit sullenly, in lost little fogs. Others are eagerly gregarious, like the portly old glad-hander who keeps returning to haunt Moyers with bad jokes and half-remembered old songs, or Eddie, who is 23 and has lived in institutions since the age of 7.

Eddie spends most of his time on camera, telling Moyers how much he wants to leave the hospital: "I act perfectly normal on the outside." We are told in a post script that he finally was released. We are also told that Dr. Bill Werner, the director of the hospital and a man who comes across as uncommonly well-meaning and realistic, died of heart attack after filming was completed. However singular and isolated himself, he had seemed a source of hope.

Throughout the program, the notion that the mentally ill and the mentally well are easily distinguished is repeatedly challenged. We see a raucous, almost violent argument in the halls of creedmoor involving complaining patients, members of their families and hospital workers. But later, on the streets of Far Rockaway, where many formerly hospitalized patients now live in a kind of halfway house hotel, we see an argument just as frenetic, unreasonable and filled with free-association among supposedly normal citizens frightened at the thought of alleged crazies walking loose on their city streets.

Creedmoor itself looks homey when compared to the now-abandoned "violent wards" that Moyers and Werner tour, although a peek through the window of the "Quiet Room" at Creedmoorsuggests that there really can be no such thing as a state institution for the mentally ill that isn't in some way demeaning and inescapably depressing.

But Elaine, one of the patients, gets out during the program, after vowing early and poignantly. "I'm going to make it this time." And later being sent off with such advice from fellow patients as "Try toforget the past." She is later seen at a club where others who have left mental institutions dance to, of all songs, "Staying Alive."

Throughout the report, Moyers talks with doctors, staff members and patients inan eye-to-eye, on-the-level style that is never condescending or melodramatically exhibitionistic. Moyers doesn't have to pretend to be concerned because he is concerned: we can tell, and the people he is talking with can tell. He has a gift for this and it has perhaps never been putto better use or to a greater challenge.

Unfortunately, this is the last "CBS Reports" with Moyers as correspondent. He has returned to public television where his new and still underfunded public affairs series will begin in January. CBS News needed him because he brought humanism and unpretentiousness to a shop that sometimes gives the impression of lacking both. One hopes the considerable constraints of public television won't give the title "Anyplace But Here" an additional meaning for Moyers.

Producer and writer Tom Spain shows guts and sensitivity with "Anyplace But Here," and Moyers demonstrates compassionate appreciation for resonant or microcosmic incidents and remarks. At the hotel in Far Rockaway, he talks quietly on a lobby bench to an old woman who has been complaining bitterly about the hotel and now says she wants to go back to the cold sanctuary of the hospital.

"Are you going to give up?" Moyers asks calmly, and when she nods "Yes," she has said something about the human condition that even TV documentaries, prefer not to admit. This is a program not about "them." but about "us." CAPTION: Picture, Correspondent Bill Moyers