By Arsheeya Bajwa and Max A. Cherney

(Reuters) - Mobile chip designer Qualcomm on Wednesday forecast third-quarter revenue that would not meet estimates, joining other tech companies such as Snap and Samsung that voiced concerns about the effects of U.S. President Donald Trump's trade war.

Qualcomm third-quarter estimates reflected the impact of the tariffs "as they stand today," Chief Financial Officer Akash Palkhiwala said in a conference call with analysts following the results. But he said the situation could change due to rapid developments in U.S.-China trade tensions.

"We do not see any material, direct impact - there is smaller direct impact and some minor changes in demand," Palkhiwala said, in reference to the tariffs. "(It's) difficult for us to predict."

Qualcomm forecast third-quarter revenue just shy of Wall Street estimates, expecting tepid demand for its smartphone chips. Apple, which is known to be Qualcomm's largest customer, has also begun to produce its own modem chips and is expected by analysts to buy fewer of Qualcomm's modems as it introduces its home-grown chips into more products.

Qualcomm's stock, which was already down more than 3% year to date, sank 6% more in extended trading, as investors have worried about global trade turmoil.

The company's chips are currently excluded from Trump's steep tariffs but slower economic growth will likely hit demand. In a securities filing on Wednesday, Qualcomm said it was uncertain about the effects tariffs and other "related actions" might have on its business.

"Tariff uncertainties will definitely have an impact to its topline outlook as Qualcomm is exposed to the smartphone, consumer IoT and the automotive end-markets," Summit Insights Group analyst Kinngai Chan said. 

For its current fiscal quarter, the company expects a sales range with a midpoint of $10.3 billion, below analysts' average estimates of sales of $10.35 billion, according to data compiled by LSEG.

San Diego, California-based Qualcomm is the world's biggest supplier of modem chips that connect smartphones to wireless data networks. 

It expects adjusted profits between $2.60 per share and $2.80 per share. The midpoint is above estimates of $2.67 per share.

APPLE-QUALCOMM 'DIVORCE'

Despite mounting competition in China's domestic chip sector, Qualcomm has retained its stronghold of the smartphone market, supplying both Apple and Chinese handset makers such as Xiaomi, Oppo and Vivo. 

However, Apple's increasing push toward building in-house modem chips threatens Qualcomm's share of the iPhone makers' silicon components. In the second quarter, Apple accounted for 27% of Qualcomm's revenue, Chan said.

"Apple’s long-telegraphed move to bring modem development in-house is less a surprise and has been more of a slow-motion divorce - with Qualcomm playing the role of the efficient but increasingly expendable ex," said Michael Schulman, Running Point Capital investment chief.

In the conference call, Palkhiwala said that Qualcomm is forecasting it will retain a 70% share in the products Apple launches in the fall, when the iPhone maker typically unveils its latest gadgets.

Schulman said he expects Apple to supply no revenue to Qualcomm by 2027.

Even though Qualcomm's chips so far have been excluded from Trump's steep tariffs, escalating Sino-U.S. trade tensions have cast a shadow over the company's revenue from its biggest market. China accounted for about 46% of its total sales in its last fiscal year. 

Qualcomm categorizes geographical revenue on the basis of a customer's headquarters. 

"As we navigate the current macroeconomic and trade environment, we remain focused on the critical factors we can control – our leading technology roadmap, best-in-class product portfolio, strong customer relationships and operational efficiencies," CEO Cristiano Amon said in a statement. 

While the U.S. government has granted smartphones and chips special exclusions from steep tariffs, Trump has warned of sector-specific levies to come for semiconductors. 

Global smartphone shipments rose 1.5% in the first three months of the year, according to data from research firm IDC, with major Qualcomm customer Apple front-loading supply to sidestep potential tariffs.

Qualcomm reported adjusted per-share profit of $2.85, edging past estimates of $2.82. The company reported sales of $10.98 billion for its fiscal second quarter ended March 30, beating estimates of $10.66 billion.

The company's licensing segment generated sales of $1.32 billion, while its chip business reported revenue of $9.47 billion. Both were ahead of Wall Street estimates.

(Reporting by Arsheeya Bajwa in Bengaluru and Max A. Cherney in San Francisco; Editing by David Gregorio)