SAN JOSE, Calif. — AT&T Inc. wiped some of the glow off Apple Inc.’s iPhone yesterday, releasing numbers that showed fewer people than expected signed up for service in the first two days of the multimedia cell phone’s release.

AT&T — the iPhone’s exclusive carrier — said it activated 146,000 iPhones on June 29 and 30, a number that disappointed investors following some analyst forecasts that Apple would sell 500,000 or more iPhones in its first weekend.

The news interrupted a steady rise in Apple’s stock price that started with the iPhone’s release. The 18-percent surge generated $18 billion in shareholder wealth.

Yesterday, Apple shares fell $8.81, or more than 6 percent, to $134.89, wiping out more than $7 billion of Apple’s market value.

Analysts cautioned against reading too much into AT&T’s activation numbers, saying the actual number of iPhones sold may be much higher but was not reflected in the figure because many users had activation problems and couldn’t sign up for a few days.

“It’s just had such a run on overexpectations, I don’t see this as any sort of disappointing metric in terms of the iPhone overall,” said Ingrid Ebeling, an analyst with JMP Securities. “I think it’s just gotten a little overhyped over the past month.”

Also weighing on Apple’s stock yesterday was a report from CIBC World Markets that said demand for the iPhone has experienced a “significant decline” in the past 10 days, a slowdown driven in part by dissatisfaction with the slow data transfer speeds on AT&T’s network. CIBC used store visits and a survey of iPhone buyers to reach its conclusions.

CIBC said it expects Apple and AT&T to boost their marketing push for the iPhone and the companies could introduce a new model in November — earlier than expected — that operates on a faster network. The two models now available cost $499 and $599.

Apple spokeswoman Jennifer Bowcock did not immediately return a call for comment yesterday.

Apple is expected to release more information on the iPhone’s sales in its third-quarter earnings report today. The company has been tightlipped about its near-term sales forecasts, saying only that it hopes to sell 10 million worldwide by 2008.

Shaw Wu, an analyst with American Technology Research, said the little information Apple is likely to release will be closely watched by investors looking for signs of the iPhone’s momentum.

“Even though it’s only two days of information, it’s definitely going to be looked at carefully,” Wu said.

Analysts are predicting Apple will continue its strong profit growth. According to a survey by Thomson Financial, the company is expected to earn 72 cents a share on $5.29 billion in revenue for the third quarter.

Apple chief executive officer Steve Jobs is predicting that the iPhone will become the company’s third major business.

Early acceptance of the combination iPod and mobile phone is crucial to Apple’s strategy to crack the mobile-phone market, which is almost four times larger than the PC market. If demand falters, Jobs may fall short of his goal to make the device the third-best after Macintosh computers and iPods.

“There’s such great expectation built into the stock now because of its valuation that a miss, if the iPhone numbers come in light, it’s going to weaken that premium mentality investors have for Apple shares,” said Mark Mowrey, an analyst at Al Frank Asset Management in Laguna Beach, Calif., which owns about 38,500 Apple shares.

CIBC World Markets said demand for the iPhone has had a “significant decline” in the past 10 days and that Apple and AT&T may try to boost demand by increasing their marketing efforts.

“We have noticed decent inventories at stores, and thin demand at best,” analyst Ittai Kidron wrote in a note. “Among the stores we visited, most visitors were not looking at the device, and only a very small subset bought it.”

CIBC’s Kidron also wrote that the iPhone, which he initially viewed as a negative for Research In Motion Ltd., the maker of the BlackBerry smartphone, may instead be a positive.

“The iPhone has significantly increased awareness for e-mail devices,” Kidron wrote. That’s “positive mainly for RIM, the brand of choice for e-mail devices.”

Kidron, who is based in New York, rates Research In Motion at “sector perform.” He does not cover Apple.

Before yesterday, Apple stock was up 69 percent this year, compared with a 15-percent gain for the Standard and Poor’s 500 Information Technology Index.

With Bloomberg News reports