Lucent Technologies Inc., a bellwether company whose equipment is a primary driver and beneficiary of the telecommunications boom, sent a shudder through Wall Street yesterday, announcing that its earnings for the quarter just ended are likely to be substantially lower than expected.

Lucent did not deliver the word until after markets closed. But in after-hours trading its stock was down by as much as 30 percent. And while analysts said Lucent's troubles are specific to the company and reflect no fundamental change in an industry defined by growth, the company holds a key place in the technology world and the news may heap fresh pain upon markets today. The tech-heavy Nasdaq composite index has shed more than 7 percent this week, after rocketing 85 percent last year.

In a statement, Lucent said earnings for the quarter ended Dec. 31 would be 36 cents to 39 cents a share, compared with 48 cents for the same quarter a year ago. Analysts had projected about 54 cents for the quarter. The company blamed its shortfall on production bottlenecks that have prevented it from satisfying voracious demand for the sophisticated systems that route phone calls and Internet traffic, and on decisions by customers to postpone purchases.

The company said the picture should improve later this year as production speeds, allowing it to meet its ambitious goals for 20 percent to 25 percent growth for the year. It vowed to capture market share from its rivals.

"We are clearly disappointed with the results for the quarter," said Lucent chief executive Richard A. McGinn. "We still expect our revenues to grow 3 to 5 percentage points faster than the overall communications networking market."

Some industry watchers said the news was no cause for panic--not for Lucent, nor the larger high-tech domain. "This is very much a blip," said Brian Adamik, a telecommunications analyst with the Yankee Group in Boston. "Lucent has got one of the finest management teams in the industry. They have a great product. There's no fundamental shift in their market. . . . We'll look back in several quarters and things will be back on track."

But others did not share that assessment. Eric. C. Buck, an analyst with Donaldson, Lufkin & Jenrette Inc., said the news amounts to an admission from Lucent that it has long over-hyped its numbers, pumping up the forecasts for its rate of growth.

"The company ran out of rope," Buck said. "They've been over-promising the growth rate. They've been stretching to make the numbers, and it finally caught up with them."

Buck said the overall market for communications network equipment is growing at about 14 percent a year. In aiming to grow faster, Lucent has effectively promised to take customers from others in the industry, such as Nortel Networks Corp. and Cisco Systems Inc. "They're not taking share," Buck said.

Lucent is a leading provider of networking gear, the machinery that runs the Internet and telephone systems. As Internet graphics and applications grow more sophisticated and users demand ever-greater speed, the companies building the networks are eager for equipment that can carry larger chunks of data faster; they are thirsting for "bandwidth."

Though Lucent has historically been at the forefront of the industry quest for greater speed, the quarter just ended reflects a subtle--some say temporary--shift. As Nortel and Cisco have rolled out new products to handle faster floods of data, Lucent has sought to leap ahead. Nortel has enjoyed tremendous demand for its latest generation of networking gear. Lucent is rushing to introduce a product with similar capabilities, but it won't be widely available until March.

Overall, Lucent said its lower numbers reflect the fact that many of its customers--a spokeswoman declined to name names--last year delayed purchases of networking gear. Some preferred to wait to see what chaos Y2K might bring. Others encountered finance problems. Still others opted to wait for even faster products that should be available this spring.

Even as analysts said the troubles were confined to Lucent, the market appeared to digest the news as bad for all in its business. In after-hours trading, Nortel and Cisco were both down sharply as well--a sign the sellers could spill throughout the technology market this morning.

CAPTION: Specialist John McGraner, left, directs trades in Lucent stock on the NYSE yesterday.