For Doris Roberts these are the days of smiles ahead and tears behind.

She is touring the country happily talking about ''Had I a Hundred Mouths," the last book written by her husband of 20 years, William Goyen, who died a year and a half ago. But the conversation turns quickly to her work on "Remington Steele," ticketed for renewal next season with Roberts aboard in an expanding role.

"I'm hoping the book will sell," she said. "I'm trying to get him to another audience. Since this is a book of short stories it may be easier to sell to another public grouping," she said of the volume of short stories. Goyen's previous work, Arcadio, was a novel about a hermaphrodite.

"One of the joys I have is that because of th fame of 'Remington Steele' . . . I have access to the media with a book of literature most serious writers would not enjoy . . . At least I can perpetuate his legacy . . . In a world of copycats and clones, to be an original is extraordinary."

"Steele" has done wonders for Roberts herself. Before she became a member of the permanent cast in the '83-'84 season she had to carry her American Express card at all times. Her face was familiar, but only the closest watchers of TV and movies would match it to the name in the credits.

Roberts has a string of stage roles going back to her Broadway debut in "The Time of Your Life" in 1955, with other credits including "The Desk Set," "The American Dream," "The Death of Bessie Smith" and "The Last of the Red Hot Lovers." There have been film appearances in movies such as "Barefoot in the Park," "The Heartbreak Kid," and "The Rose." Television parts have included roles in "Ruby and Oswald" and "It Happened One Christmas." She won an Emmy for her portrayal of a bag lady in the "Cora and Arnie" episode of "St. Elsewhere," giving Roberts her most imposing presence on TV.

That was before the part of Mildred Krebs in "Remington Steele" came along. Or rather, before she went after it.

"The part originally was to be for a woman 10 years younger," said Roberts, who'll be 55 this year. "I heard about it and asked to see it. I had my agent call and ask if I could read for it."

Actresses of Roberts' standing don't read for parts. The producer's response was, we know what she can do, but she's not right for the part. She went and read for it anyway and by her own estimate "knocked them out of their socks."

Roberts will go into her third season with an expanded role from her original casting as a secretary/office manager. She and Stephanie Zimbalist will depart for England in search of Pierce Brosnan. That's where he was heading when last seen this past season getting into the detective firm's limo.

"This year Mildred won't be chained to her desk," said Roberts. "She'll be out and about, will be a confidante of Laura and Remington and will get to know his mysterious background."

Roberts' work in "Remington Steele" is balanced with other projects she plans for the show's hiatus. She was recently preparing to do "A Letter to Three Wives" and was "shortening my nails, removing polish and wearing the wig I'll wear for my part. I'm already externalizing the part. I love doing something different," she said with delight.

"You know, a couple of years ago if you were 50 years of age you were finished," said Roberts. "Now there are 50-year-old women everywhere in show business -- Elizabeth Taylor, Joan Collins . . .Doris Roberts."