TULSA, Okla. — A pioneering idea at the start of the technology boom spawned Williams Communications Group and made its former parent company a fortune.

But neither innovation nor its affiliation with Williams Cos. could save Williams Communications from the whipsaw of mounting debt and the telecommunications meltdown. The Tulsa-based broadband wholesaler filed for bankruptcy last Monday.

Williams began in a 1985 brainstorming sessions where executives of a Williams Cos. subsidiary were wrestling with what do about miles of idle natural gas pipelines.

At the same time, long-distance phone service companies, thriving a year after the Bell System breakup, needed fiber-optic lines to carry messages.

For Williams Cos., a Tulsa-based energy firm, the opportunity to diversify into telecom was too good to pass up. It became the first company to lay high-capacity fiber-optic cables in decommissioned pipelines.

Soon, Williams Communications, then known as Williams Telecommunications, built a nationwide network and found its niche as a long-distance wholesaler, selling use of its fiber optic lines to companies like Sprint.

Rapid growth attracted a suitor in 1995. LDDS Communications, which later became WorldCom Inc., bought all but one fiber of Williams Telecommunications' 15,000-mile network for $2.5 billion.

Williams Cos. used profits from the sale to acquire Transco Energy, a large Houston-based pipeline company, and fellow Tulsa energy company Mapco Inc. It nearly tripled in size.

In January 1998, Williams Cos. announced a $1 billion effort to re-enter the wholesale broadband market, using its one remaining strand as a starting point.

Williams Cos., whose assets had grown to more than $14 billion, now had the balance sheet to back construction of a second, larger network for subsidiary Williams Communications.

The company borrowed heavily to build more fiber optic cables, hair-size glass lines capable of transmitting thousands of signals at once. The network grew to 33,000 miles connecting 125 cities on five continents.

Stock value soared, peaking at more than $40 per share in summer 2000, as the company attracted blue-chip customers and rode the telecom wave. Revenue was growing about 10 percent per year, stoking confidence among executives, analysts and investors that the young high-tech firm would soon become profitable.

The subsidiary outgrew its space in Williams Cos. headquarters, so a 15-story technology center was built next door. Fully wired for video and data transmission, the building opened in July.

"This is about who our customers are — the biggest players in the telecom business — and showing them a state-of-the-art facility, a leading-edge company that's going places," Williams Communications chief executive officer Howard Janzen said then.

Williams Cos. spun off its subsidiary to stockholders in April 2001. Janzen praised the deal, calling it then the "natural evolution of our business strategy."

But soon the telecom bubble burst and the bottom fell out of broadband prices. Investors fled as the perception grew that companies like Williams Communications had built too much cable.

As prices fell, telecom companies found it difficult to generate enough cash flow to pay creditors. Williams Communications had annual interest payments of $500 million on debts that topped $7 billion.

In September, Williams Communications sold the tower, once a symbol of its growth, back to its former parent company and leased space inside.

The company entered into negotiations to restructure its finances, and on Feb. 25 said it was considering filing for bankruptcy. To reduce costs, it cut about 800 jobs, suspended quarterly stock dividends and delayed interest payments.

The stock plummeted. The New York Stock Exchange halted trading on March 1 after Williams Communications shares had a 30-day average price of less than $1. Within weeks, they were trading over the counter for pennies.

The company's April 1 annual report revealed a negative net worth for the first time and 2001 losses of $3.8 billion.

Finally, facing a third deadline to restructure its balance sheet, the company filed for Chapter 11 bankruptcy, joining other telecoms that have filed for bankruptcy protection or have gone out of business, among them Global Crossing, Mcleod USA, 360networks, Winstar Communications and Northpoint Communications.

Williams Communications will continue operations while Williams Cos. and bondholders wrangle over how much of the company's remaining equity each will control. Stockholder equity was wiped out.

No additional layoffs have been announced, and Janzen told worried employees at a meeting Wednesday the company will emerge from bankruptcy leaner and stronger.

"What got us here was not bad performance by anybody in this room," he told employees. "We didn't have a screwed-up business plan."