A long stretch of unusual calm in the stock market gave way to a succession of violent swings in the third quarter as investors worried that the Federal Reserve would raise interest rates at last and then were disappointed — after the briefest spurt of euphoria — when the Fed demurred.

The net result was the worst quarter in four years, and some strategists predicted further trouble ahead.

“This doesn’t end happily,” said Komal S. Sri-Kumar, president of Sri-Kumar Global Strategies, an investment consulting firm. “2016 looks like a volatile and pretty difficult year for markets in the United States and around the globe.”

It was certainly a difficult quarter. The Standard & Poor’s 500-stock index lost 6.9 percent in the three months through September, closing at 1,920, roughly where the benchmark stood in May of last year.

The decline was part of a broader trend toward shunning the risky assets that had been coveted for six-plus years. High-yield bonds fell, as did many commodities.

Treasury prices rose as their yields fell during the quarter, with the return on the benchmark 10-year note dropping to 2.04 percent from 2.35 percent at the end of the previous quarter. Treasuries are often a safe harbor during turbulent market conditions, and with the Fed maintaining its target for short-term rates at zero to 0.25 percent, as it has for nearly a decade, traders saw no reason to expect the outlook for long-term rates to change anytime soon.

The Fed’s action, or absence of it, on Sept. 17 and accompanying remarks were as benign as investors possibly could have imagined. The central bank, in its statement and in the news conference held by its chairwoman, Janet L. Yellen, highlighted a slightly diminished emphasis on domestic economic growth and inflation and a more pronounced concern about developments abroad.

If Wall Street seems unwilling to take yes for an answer, investment advisers say, it’s because the Fed’s welcome caution in raising rates is more than offset by the fact that the Fed sees so much to be cautious about.

“The market didn’t expect a rate hike, and it didn’t get one,” said Katie Nixon, chief investment officer for wealth management at Northern Trust. “The problem is the tone of the minutes and press conference that suggested the Fed is worried more about the global growth outlook than previously. That’s really spooking the market.”

Laird R. Landmann, co-head of fixed income at the TCW fund-management company, agreed that central bankers were unnerving investors and suggested that they might have given themselves the jitters, too.

“There’s a mind-set that has developed at the Fed where they’re waiting for a perfect moment that never comes,” he said.

With or without the Fed’s help, enough happened in the third quarter to leave owners of stock funds feeling a bit twitchy. The average domestic portfolio fell 7.8 percent, according to Morningstar, led lower by specialists in energy and other natural resources, communications and technology.

Looking at a broad array of American economic indicators, it’s hard to see what investors are afraid of. The United States is a paragon of growth, at least by the tepid standards of the last decade, especially the job market. The unemployment rate is hovering just above 5 percent, and the number of job openings hit 5.8 million in July, the most since the federal Bureau of Labor Statistics began reporting the figure in 2000.

“There are yellow lights flashing out there in terms of the global economy, but there’s no deterioration in the U.S. economy,” said Stephen E. Kylander, manager of the RBC Mid Cap Value fund.

That should be good news for small and medium-size companies. They depend on foreign markets for a smaller proportion of their sales than big companies do, but they benefit just as much from lower interest rates. Yet mid- and small-capitalization funds underperformed in the third quarter: Midcap portfolios lost 9.4 percent and small caps lost 10.8 percent.

One reason for the weakness, Mr. Kylander said, is that while smaller companies tend to have a domestic focus, many would like to gain a foothold overseas and cannot.

But he sees value in market segments that offer decent dividend income, like utilities and commercial real estate investment trusts, and in domestically focused industries like trucking.

Shareholders in international stock funds used the third quarter mainly as an opportunity to sell, driving the average one down 10 percent. Europe displayed newfound stability over the summer as Greece ceased to be an urgent problem for the moment, but that was more than offset by deteriorating conditions in emerging markets. Funds that specialize in Latin America, Asia and diversified emerging markets had average losses of 12.8 percent or more.

Chinese stocks had an awful quarter; funds that focus on the country plunged 20.9 percent. The economic malaise there continued and may have contributed to the decline in American stocks and the limited relief experienced when the Fed stood pat.

Persistent money flows out of China forced its central bank in August to sell nearly $94 billion of foreign-currency reserves, much of it held in United States Treasuries, to try to prop up the currency, the renminbi. That would have produced an effect opposite to quantitative easing — the Fed’s substantial purchases of Treasury bonds that began during the financial crisis, ended about a year ago and are widely seen to have benefited stocks along the way.

China is a huge exporter, and with the decline in the renminbi it has begun to export deflation to other developing countries, forcing them into a difficult, maybe hopeless, position. If they weaken their currencies to match the renminbi devaluation, the burden of their immense dollar-denominated debt will grow when expressed in their own currencies. If they keep their currencies relatively strong, however, their exports will become less competitive.

“There is no room for them to maneuver,” Mr. Sri-Kumar said. He expects the developing countries to devalue, even if it leads to credit downgrades, defaults and difficulty in refinancing debt for corporate and government borrowers.

“They will have to go through with it to have fewer negative effects on competitiveness,” he predicted.

It’s a no-win situation. Mr. Sri-Kumar noted that emerging markets accounted for more than half of global economic output. They’re not the small, exotic growth stories of 10 or 20 years ago.

If those countries slow because of this crisis, “eventually it’s going to reverberate back to the United States,” he said.

Mr. Sri-Kumar predicted a year ago that the Fed would hold rates steady this year, and fragility in the developing world has persuaded him to extend his forecast through 2016. That could leave the stock market in a bad spot, in his view, as investors, desensitized to the putative benefits of ultra-easy monetary policy after nearly a decade, sell into any short-lived rally after the Fed postpones a rate increase, as it did last month.

He recommends sheltering in high-quality bonds and blue-chip stocks that pay generous dividends.

Nothing goes down forever. At some point, perhaps in the first quarter, emerging stock markets will be cheap enough to present a low-risk buying opportunity, he said.

Rebecca H. Patterson, chief investment officer of Bessemer Trust, a firm that advises wealthy families, expects a shorter wait for the Fed to move.

“The Fed is still looking at raising interest rates at some point in the coming months,” she said.

Ms. Patterson encourages investors to have a relatively heavy allocation in American stocks while they wait, particularly in financial services and consumer discretionary companies, and remain light in emerging markets and energy. She would also be comparatively light in bonds, although she finds mortgage-backed securities to be sound bets, she said, because they are less sensitive to rising rates and she detects consistent improvement in the housing market.

Ms. Nixon at Northern Trust has a similar view of American and emerging markets: heavy in the first, light in the second. She also advocates a more modest than usual bond allocation. As for the Fed, it “wants to get off the zero,” she said, but “the job isn’t going to get any easier” given the global backdrop. So “if the Fed hikes, it may be one and done,” she said.

Mr. Landmann at TCW contends that the Fed is content to keep rates where they are.

“They’re looking for reasons not to tighten,” he said. “It’s hard to believe, at any given meeting coming up, that we have more than a 50-50 chance of tightening if things stay as they are.”

But with rates so low, Mr. Landmann cautioned, if conditions deteriorate in China and elsewhere and begin to weigh more heavily on the American economy and markets, there will be little the Fed can do. For six years, investors have bought stocks after declines. Now might be a good time to sell after rallies, he advised.

“If you’re a conservative, value-oriented investor, when prices go up you want to use it as an opportunity to take risk out of your portfolio,” he said. “Asset prices can’t stay high forever. There may be decent returns for the next quarter as the Fed stays on hold, but even that won’t work after a while. The rest of the world may take matters into their own hands. It may not matter what the Fed does.”