NEW YORK (CNN/Money) - Lucent Technologies Inc. Tuesday lowered its sales forecast for the current quarter and said it will take longer to restore profitability because customers are ordering less equipment amid a weak economy and accounting probes.

Shares Lucent (LU: Research, Estimates), the world's biggest telecommunications equipment maker, tumbled 66 cents, or more than 10 percent, to close Tuesday trading at $5.65, following the announcement and a ratings downgrade by Standard & Poor's.

Lucent it now expects a small rise of up to 10 percent in sales for its second fiscal quarter from the first quarter, instead of the 10-to-15 percent increase it previously forecast. But sales still will be down about 25 percent from the year-earlier quarter.

Lucent's lowered guidance is just one thread in a skein of bad news for telecom companies that has left Murray Hill, N.J.-based Lucent struggling to catch up with competitors in a weak economy. Shares of WorldCom (WCOM: down $1.08 to $7.93, Research, Estimates), the long-distance phone service provider, fell after the company revealed that the U.S. Securities and Exchange Commission had launched a probe into its accounting practices.

Additionally, Nokia (NOK: down $1.41 to $22.09, Research, Estimates), the world's biggest mobile phone maker, issued a lower-than-expected first-quarter sales forecast even though it expects to meet or exceed earnings expectations.

The gloomy outlook prompted ratings firm Standard & Poor's to cut its corporate credit rating on Lucent, which were already at "junk" status, to single-'B'-plus from double-'B'-minus, noting the company has about $3.3 billion in debt outstanding. The ratings outlook is stable.

"Lucent's financial flexibility is expected to remain adequate for its operational needs as it continues to adapt to challenging market conditions," Standard & Poor's credit analyst Bruce Hyman said.

Still, after the market close Tuesday, Lucent announced it would seek to raise $1.5 billion through the sale of convertible securities for use in general corporate purposes. Convertible securities generally can be exchanged in the future for shares of newly-issued common stock.

The company also said Tuesday that market uncertainty likely will push Lucent's return to profitability and positive cash flow into fiscal 2003 and that second-quarter results would match earlier forecasts. The company plans to update guidance on April 22, when it releases its second-quarter results.

"Only in the last couple of weeks have we seen the effects of a general tightening on spending that has caused us to modify our expectations," Lucent CEO Patricia Russo told analysts during a conference call Tuesday. "We still see growth, but we thought it prudent to share that we see a tempering."

Lucent said second-quarter results, excluding a charge, will match its earlier forecasts. Lucent cut its work force from 106,000 last January, excluding the former Agere Systems Inc. unit that was spun off, to 62,000 at the end of last year as it cut costs to cope with declining sales.

"You only have to read the daily business news in the last few weeks to understand that this is a market issue, not a Lucent issue," Russo said.

Russo said that it's just a matter of timing where its customers' ordering is concerned, and that the company still anticipates 20 percent margins in 2002 and 35 percent margins by the end of 2003. However, the business slowdown will force Lucent to push back its planned break with Agere into the third quarter.

"I think what we're seeing is a much tighter holding on spending than we would have expected," Russo said. "It's really a general tightening that we've seen across the board that's been commensurate with releases we've seen in that time period."

Agere, which makes communications semiconductors, was Lucent's microelectronics unit before it went public last year.

Despite lower sales, Russo said Tuesday that product schedules remain on track, and Lucent announced a series of multiyear agreements it expects will boost sales and profitability going forward.

"The progress we are making with our restructuring program will enable us to deliver the fifth quarter in a row of sequential improvement in the bottom line," Chief Financial Officer Frank D'Amelio said. "However, large service providers continue to reduce or defer their spending as they rethink their business plans and conserve cash, which is having an impact on our top line."

The company also said Tuesday it still is considering new financing, such as a bond offering, to shore up its balance sheet and improve liquidity.