TOKYO—Most Asian stocks fell Monday, sending the region’s benchmark index to its worst first-half in 16 years, on speculation rising commodities prices will erode earnings and as a stronger yen hurt Japan’s electronics exporters.

Samsung Electronics Co. led technology shares lower after Lehman Brothers Holdings Inc. cut its share-price target and crude oil climbed above $142, close to a record. Sony Corp. declined to the lowest in almost two months after the yen rose to a three-week high. BHP Billiton Ltd., the world’s largest mining company gained after oil and metals advanced.

“Oil at $150 is in sight, steel is rising, and there’s a limit to how much manufacturers can pass on the higher costs to their customers,” said Hitoshi Yamamoto, chief executive of Tokyo-based Fortis Asset Management Japan Co. “Commodities and related stocks are so strong, it’s difficult to buy anything else.”

Five shares fell for every four that rose on the MSCI Asia-Pacific Index, which added 0.4 percent to 137.46 in Tokyo. The dollar-denominated benchmark, whose value is affected by changes in regional currencies, is set for a first-half loss of 13 percent, the worst performance since a 23-percent drop in the same period of 1992, when Japan’s asset bubble was deflating.

China’s CSI 300 Index lost 0.9 percent, completing a 23-percent rout since the end of May for its worst month on record. Japan’s Nikkei 225 Stock Average dropped 0.5 percent to 13,481.38. Most Asian indexes fell after Citigroup Inc. analysts said Asian stock markets will extend declines in the second half as a slowing global economy dampens earnings growth.

“Uncertainty over the outlook for the US economy is rising again,” said Hiroshi Morikawa, a senior strategist at Tokyo-based MU Investments Co. “Investors are caught by doubt and fear.”

Samsung, Asia’s biggest maker of chips, mobile phones and flat panels, dropped 2.8 percent to 625,000 won, while Hynix Semiconductor Inc., the world’s second-largest memory-chip maker, lost 3.7 percent to 25,000 won. Lehman cut its share-price forecast for Samsung by 15 percent and lowered its target for Hynix by 11 percent, citing a slowdown in the memory market.

Sony fell 4.1 percent to ¥4,640, the biggest drag on the MSCI Asia- Pacific Index. Last week the company’s mobile-phone venture with Ericsson AB said declining sales and delays to new products wiped out second-quarter earnings.

Sony also declined after the yen strengthened to as much as 105.76 against the dollar from 107.09 at the close of stock trading in Tokyo last Friday. Gains in the Japanese currency reduce the value of repatriated overseas sales.

MSCI’s regional index lost 8.3 percent this month, resuming its 2008 decline, as record oil worsened the outlook for global economic growth and concern grew that credit-market losses may widen. The benchmark is on course for its worst monthly drop since January, when it sank 9 percent. Stock-market losses worldwide this year have wiped out about $9.2 trillion, according to data compiled by Bloomberg.

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TOKYO—Most Asian stocks fell Monday, sending the region’s benchmark index to its worst first-half in 16 years, on speculation rising commodities prices will erode earnings and as a stronger yen hurt Japan’s electronics exporters.