Samsung became the biggest smartphone brand on the popularity of earlier Galaxy models. But Apple’s release of larger-screen iPhones last month neutralized a key advantage of Samsung. Although Samsung’s phones are still slightly larger than the iPhone 6 and iPhone 6 Plus, the gap has narrowed enough for Apple to lure many Americans who liked the bigger Galaxy phones.

In a preview to earnings due out this month, Samsung Electronics Co. on Tuesday said its estimated quarterly operating income has fallen to its lowest level in more than three years, dragged down by weak sales of its flagship Galaxy phones.

SEOUL — The world’s biggest manufacturer of smartphones is feeling the intense competition from Apple Inc. and upstart Chinese brands.


Meanwhile, in emerging markets such as India and China, local brands are making inroads into Samsung’s business, analysts say.

Analysts have repeatedly cut forecasts of Samsung’s profit this year as Galaxy sales lagged expectations. They say earnings in the quarter ending in September could suffer their biggest decline in Samsung’s recent history.

In Tuesday’s report, Samsung said the median forecast of July-September operating income was $3.8 billion. That was below the median of analysts’ expectations, according to FactSet, a financial data provider. It would be a 60 percent plunge from its record a year earlier.

‘‘The operating margin declined due to increased marketing expenditure and lowered average selling price,’’ Samsung said in a statement. The company said it ‘‘cautiously expects increased shipments of new smartphones and strong seasonal demand for TV products.’’

Samsung estimated sales for the July-September period declined 20 percent from a year earlier to $44.2 billion. That was slightly below analysts’ expectations.

The company needs to revamp its handset designs, said Lee Seung-woo, an analyst at IBK Securities Co.

‘‘Rather than seeking stability, Samsung should seek to distinguish (its phones) with Galaxy’s design policies,’’ he said. ‘‘The iPhone 6 will be a significant threat to Samsung.’’


The company moved the launch of the Galaxy Note 4, a large smartphone with a stylus, to late September from October after Apple unveiled the iPhone 6 Plus.

It also began sales of the Galaxy Note 4 in China last month, getting a few weeks’ head start over Apple in the world’s most populous country.

Last month, Samsung also received upbeat initial responses to its Galaxy Note Edge smartphone, which has a curved side screen that can display weather, news, apps, and other information. But the supply of the Edge smartphone will be limited, analysts said.

With growth momentum in smartphones sagging, Samsung is moving to step up its presence in semiconductors.

This week, Samsung announced a $14.7 billion investment plan to build a semiconductor fabrication plant in the South Korean city of Pyeongtaek. Construction will begin before the summer and begin operations during the second half of 2017.

Samsung did not disclose net income or divisional earnings in its quarterly earnings preview.