When Susan Harding left her position as general manager of Newsweek's Canadian edition in New York a year ago, she was headed for greener pastures -- a Gaithersburg company that publishes three magazines about horses.

Now Harding, 42, has been promoted to executive vice president and chief operating officer of the company, Fleet Street Publishing Corp. In her new post, she is responsible for the day-to-day management of Fleet Street's publications, overseeing circulation, advertising and production.

Fleet Street, which has 45 employees, was founded 14 years ago by the company's 44-year-old president, Ami Shinitzky. The company started out publishing a newsletter about polo and now calls itself "the horse information company," with three magazines: Equus, a glossy monthly, and Polo and Modern Horse Breeding, which are published 10 times a year.

Equus is the most popular of the three, showing well in competition with the more than 200 other horse-related magazines being published in the United States. Equus has a circulation of 108,000, while Polo and Modern Horse Breeding have unaudited circulations of 6,000 each.

While other publications zero in on a particular breed or style of riding, Equus has changed the nature of the horse publication industry, Harding said. "Equus is much more focused on the horse itself," Harding said. "It's a horse health-care publication, with articles on how the owner can take better care of the horse."

The 96-page February issue of Equus includes a story on the legal aspects of owning a horse, an article on why the horse submits to man, and an examination of the relationship between a mare and a foal before and during birth.

In her new position, Harding wants to get more involved with the editorial aspects of the magazines and with "the overall balance and opportunities for the future."

According to Harding, competition for readers' leisure time has caused Fleet Street to tighten the reins and to consider shortening its stories. Cable television programs about horses also have begun to compete for the free time of the audience for Fleet Street's publications.

Harding also wants to reach a larger audience for all three publications. "We want to make the audience more aware of the publications," she said.

"With Equus, that means reaching those who are new in the horse market, and with Polo you have a lot of people who are just becoming active in the sport."

The company is always "looking for more publications," but Harding doesn't expect to add any to the Fleet Street stable soon. For the time being, Harding is savoring the opportunity of running a small magazine.

"It's definitely the most challenging job I've had," Harding said. "There's a real difference in your ability to make things happen."