The old Janet Margolin was a bit of a drag. Not objectionable, really. In a way that was part of her problem. Her screen presence was vague and passive - she was up there on the screen but never seemed to animate it. At best she appeared prettily, wistfully inert.

I had missed Margolin's recent dramatic roles on television, so her vivid, humorous perfomance as the farfetched femme fatale of "Last Embrace," a handsome but poorly plotted new mystery thriller, was a suprise. Suddenly she was fun to watch. Somewhere along the line a forceful and entertaining actress had emerged from the timid, indifferent phantom.

Margolin herself is totally conscious of the change, and if she now looks vibrant and appealing on screen, the effect is enhanced in person. She seems to glow with confidence, enthusiasm and good humour. Her head is perched forward expectantly, her huge eyes bright with interest and concentration, and quick, infectious laughter bubbles up though the swift, eloquent currents of her talk. "I've become joyful about acting," Margolin said. "It's been happening over the last four or five years, but the different astonishes people who haven't seen me for a while I doubt if people who remember only 'David and Lisa' would recognize me as the same Janet Margolin. I'm not in some respects. Now I know what I'm doing. I never knew how to act back then.

"It's interesting to discover these things in your 30s. My 20s were perfectly miserable I wasn't simply ignorant about acting. I didn't know how to read. I didn't know how to add. I had gone to one of those progressive schools where they thought that if you resisted learning something, it was best to drop the subject until you expressed an interest in it. By the time I transferred to a fairly competitive public high school, I realized how ignorant I was and tried to conceal it.

"For a while I managed to sleepwalk through.My early acting was like sleepwalking. I'd been cast in a Broadway show when when I was 18 and got incredibly good notices. That attracted Frank and Eleanor Perry, and they cast me as Lisa immediately. I wanted the role and knew I could play it, but it made no artistic demands on me. At that age I made the necessary emotional connections instinctively. It was easy, but I knew I wasn't acting.

"I'd grown up in a theatrical atmosphere in New York. I knew I hadn't paid my dues, and it didn't seem fair. I imagined myself being resented by the real actresses: 'Yeah, Margolin, another little upstart! She'll never last.' I feel the same thing now when producers ignore me and other trained actresses in order to audition a new horde of models or pin-up girls. Which is great for the producers, right?

"Knowing how lucky I'd been and how unprepared I was, I wanted to run away. And I did. I just happaned to do it on the screen, where everyone could see. I decided that the safest thing was to make as little noise and be as invisible as possible. I became that withdrawn little creature you don't quite rememberfrom 'The Greatest Story Ever Told' and 'Nevada Smith' and 'Enter Laughing" and all those other movies."

Margolin recalls "Morituri," an espionage thriller made with Marion Brando and Yul Brynner in 1964, as the low point of her fadeout. "I was 21 at the time," she said, "and petrified anyway. When the ego battles got underway, I had no desire to be caught in the middle. It seemed better to run and hide when the actors only seemed interested in doing terrible things to each other and competing for absolute authority on the set."

She returned from "Morituri" to go straight into psychoanalysis. That helped, and she believes she might have stabilized herself earlier if she had followed through on the one enjoyable filmmaking opportunity that came up - playing opposite Woody Allen in his first feature, "Take the money and Run," in 1968. "I'd had a good time for a change," she said, "and I should have seized on that trusted it. Instead, I went off and got married, and that didn't work very well. I returned to California and had a hard time getting work until I was about 30."

During one extended full Margolin entered UCLA and began studying toward a degree in sociology. "It wasn't easy for me," she said. "I kept thinking that every kid I saw out of corner of my eye would recognize me and begin sniggering about how Janet Margolin's career had fizzled out. But I was so insecure that I also worked harder than I ever had before and did very well in school.

"College also taught me how much I valued acting. After I'd been studying seriously, the things required of a person headed for a career in the social sciences began to look less interesting, and less difficult, than the things required of a truly imaginative actress. "I was still a little reluctant to take the final step and go back to acting school, There was that paranoid movie playing in my head: I get up to do an exercise, and everyone in the class is whispering, 'There's Janet Margolin; she doesn't know how to act.' Of course, there was no one but me supplying the dialogue. I had to swallow my pride and acknowledge the fact that I needed the schooling. And wanted it desperately.

"Acting school got me back in the company of actors again, and for the first time I seemed to thrive in their company, to be one of them. I'm sure the job offers hadn't dwindled away just because my work was considered unsatisfactory. It's a socia, art, and you're obliged to develop some rapport with your fellow actors and your employers. I think there was a general feeling that Margolin was not only no great shakes on the screen ,she was no fun to have around on the set.

"I knew that something had changed after James Farentino and I did some nice work on a 'Police story.' They asked us to revive the characters the next season, so someone had to have said, 'Let get Margolin back,' right? The role didn't look like anything on paper. Just one of the incessant small naggy roles I was getting at the time. Jimmy was a vice squad cop posing as a pimp, and he had began to behave like a pimp in his private life. I was his girl. It began as three little naggy scenes but we were allowed to play with it and work with it, and we made it really interesting."

Margolin edged back into movies with a small role as Woody Allen's wife in "Annie Hall" and played leading roles in several TV movies, notably "The Great Triangle Disaster." She came into "Last Embrace" shortly before the production was scheduled to begin. The star, Roy Scheider, and the director, Jonathan Demme, had different leading ladies in mind. They reached an impasse that could be resolved only by turning to a compromise candidate, who turned to be Margolin.

It appears that she may have done much more for "Last Embrace" than the movies, given its messed-up exposition, can do for her. It's an amusing irony that Margolin has made an impressive film comeback portraying a schizophrenic heroine, although a far more diverting and volatile specimen than dear soulful Lisa. She also appears to have fused the sex appeal Scheider evidently considered essential with the comedienne's playfulness that Demme ardently desired.

"In my slow new climb," Margolin said "I didn't expect a lead that fast. "Last Embrace" is the kind of film my recently former agent would never have thought of promoting me for. In fact, I asked him about it when three or four friends who had access to the script asked if I were up for the role of Ellie. He told me, 'Oh, no, they want an American beauty rose.' That's the kind of sweetie he was. Eventually, I learned that Jonathan had rejected me at an early stage because he felt I was too good-looking for Ellie. All a matter of taste, huh?

"Anyway, I kept hearing about the role often enough to believe some divine coincidence might be bringing me and it together. I was careful not to solicit it myself. As far as I knew, Jonathan and Roy were still holding out for their first choices. Another coincidence led to me begin cast. I ran into Pual Le Mat, who had just worked for Jonathan in "Citizens Band," at the supermarket. Pual also mentioned Ellie and 'Last Embrace.' He said the part was available, suited me to a T and offered to put in a good word with Jonathan."

She likes the job she did, but feels there is still something missing. I don't think Roy and I ever got close enough to make sense of the love story. Maybe there just wasn't enough time to create the necessary rapport. We were perfectly cordial, but things just didn't get percolating. There's a love relationship in the script, tortured as it is, but the characters on the screen don't really suggest it. I'd almost forgotten the wonderful luxury of film acting, though. By the time I'd finished preparing Ellie, I'd lived with the character so intensely that I was ready to go over the edge. When we began to shoot, I had to keep reminding myself to calm down."

Margolin looks like she's raring to go, uniquely primed at the age of 35 to play dozens of complicated, entertaining and possibly endearing working girls, if only the roles werw sufficiently plentiful.

"I've been studying hard, and I want it to pay off," she said. "I'm a character actress as opposed to a movies star. The character allows me to go out on a limb, and I need to find that person before I do my best work. I won't return to playing harpies on 'Starsky and Whatshisname,' which is what my exagent thought I was cut out for. The better movies people don't want someone who's been whoring it up for years on episodic television anyway.

"I want to feel that old arty buzz. You know, you're out there, and the adrenalin is pumping and your nerves are tingling and you're on the same intimate wavelength with the other actors. It's exciting and scary."