PORTLAND – When Stephen King launched his serial novel “The Plant” into cyberspace last July, he set off a wave of speculation about the publishing industry’s future in a marketplace where author and reader can do business directly, with no middleman.

Now that he has put his Internet experiment on indefinite hold, the horror writer may have lowered expectations about the future of online publishing.

In a message posted on his Web site, King told readers he was taking a break from “The Plant” to devote time to other projects but indicated he would resume work on the novel in a year or two.

King’s decision came before his receipt of disappointing figures which revealed only 46 percent of those who downloaded the latest installment paid for it, according to Marsha DeFilippo, his assistant in Bangor.

At the outset, about 75 percent of readers obeyed the honor system, shelling out $1 for the first installment, either by credit card, check or money order. The price went up to $2 for Part 4, which is longer. Part 5 was recently posted and Part 6, to be offered for free, comes out later this month.

“We did see a trend. With each installment, the numbers did go down,” DeFilippo said. She said payments for the first four parts totaled more than $500,000, but had no specific figures on the number of downloads per installment.

In messages posted on King’s Web site, some readers said they disliked the month’s wait between installments. Some said they downloaded Part 1 for the novelty and others said they gave up on the book because the price went up.

King warned at the outset that he might pull the plug if readers refused to pay up, dampening surprise at his decision to suspend the experiment after the sixth installment.

“This was a lark for him, and now he’s going back to his day job,” said Karen Jenkins Holt, managing editor of Book Publishing Report, a trade newsletter in Stamford, Conn.

Holt and others saw little likelihood that major authors, including top names like King and John Grisham, would abandon their publishers in favor of direct sales in the event that electronic publishing catches fire.

Even if they no longer printed and shipped books, publishers still would play an important role in culling through manuscripts, editing and promotion, Holt said.

“If publishers can take comfort in anything, it’s knowing that even somebody like King needs the marketing muscle of a publishing house,” said Nora Rawlinson, editor of Publishers Weekly.

Even when authors opt to sell their work online, publishers may find a way to get a piece of the action.

“There is a role for publishers, but it’s going to shift from being a retail role to more of a direct-response role,” said Lorraine Shanley of Market Partners International, a New York-based consultant to the industry.

King was not available for comment, but his assistant said the author never viewed his experiment as a threat to the publishing industry. “It was just another venue for getting his work out,” DeFilippo said.

She suggested the disproportionate attention given to King’s experiment appeared to frame it as a test of whether online publishing will succeed or fail.

“Personally, I would not think that this would be the demise of the e-publishing industry,” DeFilippo said. “I would certainly hope that it would not hinge upon Stephen King.”

Tom McCormack, retired chairman and chief executive officer of St. Martin’s Press, said Internet publishing might work for books at opposite ends of the popularity scale, but not the 99 percent in between.

“It’s likely to succeed if it has the name King or Grisham on it,” he said. “And some small book on the insects of northern Wisconsin in the 18th century, you could sell 300 copies. In the middle, things become impractical.”

Despite his admiration for King’s inventiveness and daring, McCormack remains skeptical about the prospects of e-books making much of a dent in the industry. “People aren’t going to be reading books off a screen,” he said.

McCormack said the reasons why King suspended work on his novel about a carnivorous vine that takes over a publishing house remain fuzzy, but he doesn’t think the drop in payments could be the sole factor.

“He doesn’t need the money,” McCormack said.

King’s Web site said other projects that led him to shelve “The Plant” included collaborating with Peter Straub on “Black House,” the sequel to “Talisman,” and completing two new novels. The first, “Dreamcatcher,” is slated for publication in March.

Shanley suggested that King became bored with his online serial venture, and perhaps was dispirited by the difficulties of maintaining sales without an intensive marketing effort to remind readers to return to his Web site.

“He actually got a remarkably good response rate over time,” she said.

Industry watchers said King deserves high marks for putting issues such as online publishing on the front burner and focusing public attention on the world of books.

“I don’t think anyone would fault him for everything he has tried and for really lighting the path for everybody,” Shanley said. “He has allowed us to think through some of these issues and to act as a kind of lightning rod for discussion.”