LOS ANGELES (AP) – Jimmy Smits, a proven TV star in "LA Law" and "NYPD Blue'', is looking like the go-to guy when a drama's juicy guest role demands leading-man heft.

In the final season of "The West Wing'', he was a Latino politician who becomes the first minority US president.

In the new season of "Dexter'', Smits is a prosecutor who moves swiftly and dangerously to the centre of Dexter Morgan's dark world.

Assistant D.A. Miguel Prado is a man on the right side of the law, familiar territory for Smits. But there's a "variety of different notes" to play with Prado, the actor said, which drew him to the role and story that unfolds over the third season.

"The character is something different than I've done before on television and what television audiences are used to seeing me as," Smits said.

Producers of the wryly grim drama promised that "I was going to have fun. And that's been played out in such a great way."

Prado himself is mired in tragedy.

His brother has been slain and the assumption is that a serial killer named Freebo is the murderer.

But viewers are privy to the fact that the guilty party is Dexter (Michael C. Hall) – the blood-spatter expert who regularly makes a mess taking justice into his own hands.

This time, however, his target was Freebo; Prado's sibling happened to get in the way.

Prado enlists Dexter's help to make sure Freebo is caught, while Dexter must get to him before police detectives do. The prosecutor and the forensics expert-cum-killer are fatefully linked.

"They go through this journey where they're interfacing professionally and that leads to a deep friendship that's brotherly in a lot of ways," Smits said.

As the story twists and turns, that relationship "lets Dexter open up in ways the audience hasn't seen."

Smits called it a "testament to Michael's work" that viewers find themselves rooting for a disturbing character.

Besides Hall ("Six Feet Under"), the Showtime series' cast includes Julie Benz, Jennifer Carpenter, CS Lee, Lauren Velez, David Zayas and James Remar. Its executive producers are Sara Colleton, Clyde Phillips and Charles H. Eglee, who worked with Smits on "LA Law''.

Given Smits' rich TV resume – from "LA Law" in the late 1980s to last year's short-lived "Cane" – it comes as a bit of surprise to realise that "Dexter" is his first cable series.

When asked about it, Smits points to changes in TV.

These days, broadcast networks are more likely to put on reality series or formulaic crime shows (think "CSI: Crime Scene Investigation") than an envelope-pushing drama such as ABC's "NYPD Blue" was in its day. That's created an opening for cable.

"I see it like fertile land for good writing, for exploration of character in different ways," Smits said. "Networks are boxing themselves in in terms of what they're doling out to their audiences."

The police procedurals that are among the top-rated network series represent a "very closed, basic kind of common-denominator thing. They are popular and do well, but you're just able to explore more of a landscape on the cable networks."

Smits sounds bemused by his "Dexter" billing as "special guest star" – "It sounds like something on a Quinn Martin production out of the '70s" – but he represents a coup for the series, as his casting did on "The West Wing''.

When NBC's White House drama wrapped in 2006 with his character, Democratic Rep. Matthew Santos, defeating Republican rival Sen. Arnold Vinick (Alan Alda), Smits looked downright presidential.

Some observers, Smits notes, see echoes of that race in the contest between Republican Sen. John McCain and his African-American competitor, Democratic Sen. Barack Obama.

The actor is finding the real-life contest addictive.

"If you had to ask me what my TV diet has been in the last few months, I would have to say this ongoing miniseries that I've been watching called `Election '08'," he said.

"That's been my little soap opera, my guilty pleasure."