THE title page of ''Morning Glory'' lists Julia Cleaver Smith as its author. But Julia Cleaver Smith is really two people - Diane Cleaver and Nikki Smith. ''Morning Glory'' (New York: Pocket Books, $3.95 paperback) is a family saga about three generations of strong-willed women in the Harlow family. It is set in a small town in northeast Texas in a period spanning from 1917 to 1975, when the main character, Amelia Bliss Harlow, builds a publishing and communications empire.
Amelia runs her empire and her family with an iron hand. The climax of the novel is a much-publicized trial in which Amelia fights for the custody of her granddaughter and heir, Kate Morning Glory Harlow.
Cleaver and Smith say their plot was inspired, in part, by the famous Gloria Vanderbilt custody case, described in Barbara Goldsmith's book, ''Little Gloria . . . Happy at Last.''
They were intrigued by what would drive a child to say, ''I never want to see my mother again.''
They chose Texas as their setting because they wanted something expansive. Neither author has ever lived in the state, but both have visited it often. As the backdrop for ''Morning Glory'' they selected the publishing field because it is an area that interests both of them and in which they have spent their entire careers.
Ms. Cleaver, a Briton, has worked for Doubleday, Straight Arrow Books in San Francisco, and Simon & Schuster.
Ms. Smith, originally from Washington State, has worked for a publishing division of Columbia Teachers College, New York University Press, Atherton Press , and Horizon magazine. She was also cofounder of a small now-defunct publishing house that brought out Sam Shepard's first plays.
Both authors currently work for Sanford J. Greenburger Associates, a New York literary agency.
Interviewed recently here in New York, Cleaver and Smith described their method of collaboration. Ms. Cleaver says, ''We talked a lot. The book was talked out all the way. . . .
''We wanted to create a voice that belonged to neither of us,'' she continued. ''If Nikki had written the book or if I had individually, it would be a very different book. What we wanted was an integrated third voice - Julia Cleaver Smith.''
Their starting point was a 109-page plot outline, complete with character sketches, that was sold to Pocket Books in 1980.
When they actually started writing the novel, they divided the outline into sections, worked individually, then swapped sections and made comments, criticisms, and changes.
They never felt it was necessary to sit down in the same room and work together. At the office they could have quick conversations about the book as the writing progressed.
Nevertheless, with both Cleaver and Smith engaged in their full-time jobs, the project, which included major revisions and the rewriting of the second half of the novel, took them three years to complete.
Both Cleaver and Smith say they are very pleased with the final result. Their only regret - and it is minor - is that the book was published in paperback rather than hardcover.
''A hardcover book has more cachet . . . ,'' Cleaver said. But she added, apologetically, ''I hate to think that I have that in me; I'm always (asking) authors, 'Would you rather have 7,000 copies of your book sold or 100,000?' . . . There's still that part of me that feels a bit cheated.'' Smith added, ''We are both of, in, and out of this profession when it comes to this book. . . . I think we made the correct professional judgment. . . . We wanted to be perfect, understanding authors . . . having listened to authors complaining and complaining, no matter what. So we said yes (to the paperback offer). . . . The other half of us regrets it.''
Cleaver continued, ''I'm very proud of the book. I'm proud that we finished it, and that we can be pleased with it, and that we actually worked together. I think that's a great achievement.''