In the beginning, Helen Mirren wasn’t sure she could pull it off.

Understand that this is a woman who has done it all – at least all that was worth doing – so this crisis of confidence was unusual.A working actress since she was 18 and a veteran of the Royal Shakespeare Company, she can go regal and classical, or steam up the screen as she has in a series of offbeat films including “The Long Good Friday” and “The Cook, the Thief, His Wife and Her Lover.”

Mirren, 47, the London-born granddaughter of a Czarist army officer (she was born Illynea Lydia Mironoff), is at the top of her game, an actress who can be earthy and sexy and funny and as nasty as she needs to be. But she didn’t know if she could play a cop, this particular cop anyway – Deputy Chief Inspector Jane Tennison in “Prime Suspect,” which was seen on public TV’s “Mystery!” series last year and in Great Britain before that. You will look a long time before you will see a better sustained performance than Mirren’s in “Prime Suspect,” which is now being repeated on “Mystery!” and leads into “Prime Suspect 2,” a new Jane Tennison story that begins Feb. 11 with a four-week run. “I was nervous, not at all sure of myself,” she says of taking on the character. “An actress rarely has to be in a situation of having to take control of a group of men with your voice and your body language.”

Doing research, Mirren met a couple of women police inspectors in London and remembered how “I was observing them observing me. I tried on a costume in the mirror and folded my arms because you have this idea that you’ve got to look strong. But one of them said, `Incidentally, we never fold our arms. It’s defensive.’ “I try not to make a big deal out of this whole thing about women’s roles, because life is tough for actors and actresses in general. But what (“Prime Suspect”) showed is that you could write a great role for a woman who is not a victim or that slightly American idea of a tough businesswoman – that you can be ambitious and be very vulnerable.” With her eccentric career path, Mirren is infinitely respected by her peers, but not that well known to the public. Despite the range of her work, this is the role of her life, and she knows it.

“Prime Suspect 2” is as good as if not better than “Prime Suspect” because of the way Tennison has changed. This isn’t Columbo or Perry Mason, stories where there is no life, only plot. “Prime Suspect 2” shows how far she has come, and running the two miniseries back to back makes it clearer than it would have been otherwise. When the body of a young woman is found in the garden of a London home, the investigation is complicated by the acrimonious relationship between the mostly white police and the West Indian and black community in which the body was found. Tennison supervises the investigation, which is made even more sensitive by the fact that her boss is up for promotion.

Also named to the case – against Tennison’s wishes – is a black officer with whom she recently had an affair, a mixed-race romance handled in a matter-of-fact way. By comparison, the American networks would have hurt themselves hyping it. In the first story, Tennison was a dogged and ambitious detective. A woman on the way up who admitted no public weakness, which was reflected in her look – a severe haircut, a minimum of makeup, dark, functional suits and a serious smoking habit. You could practically feel her frustration at being held back because she was a woman. If anything, she was too tightly wrapped, loosening up only in private moments, and then only briefly by fluffing herself up in front of a mirror before, say, an important meeting.

In the sequel, she is still the dedicated detective, but she’s more comfortable with herself. She is used to authority now. She knows she commands respect and doesn’t need false bluster, though you’d never mistake her for one of “Charlie’s Angels.” Tennison has stopped smoking, her hair is softer, and her clothes have bolder colors that reflect her self-assurance. “She is more at ease with her circumstances,” says Mirren, who has a way of talking about Tennison as if she were a real person and not a character. “She has won certain battles and is a lot more relaxed with her position. “In this kind of situation, where you come back to it once every year and a half or so, you change within yourself, too. So she is going to change and develop over the three or four years that I’m playing her because I have changed.”

By the way, there will be a “Prime Suspect 3,” probably sometime in the second half of 1994. After that, it’s over. Maybe. “When we did the first one, we planned that if it was a success to do two more,” she says. “A third is being written at this very moment.” The character is so internationally popular that movie rights were sold almost immediately. According to Mirren, there already has been a script written at Universal – though, incredibly, she probably won’t get the change to do it. “It’ll be an American story, so it’s kind of unlikely, isn’t it,” she says with a fatalistic shrug. “Would I like to do it? I’d be a liar to say no, and I’m not going to lie. I’d love to. She is all mine now.”