(In Aug. 31 story, paragraph 4, corrects firm name to SpiderRock, from SpringRock)

* Zoom tumbles on faster-than-expected drop in demand

* Apple off lifetime high, as tech broadly weighs

* All main indexes post solid monthly performances

Aug 31 (Reuters) - Wall Street's main indexes closed marginally lower on Tuesday, although the slightly subdued ending to August failed to detract from a strong monthly performance in what is traditionally regarded as a quiet period for equities.

Having all posted lifetime highs in the second half of the month, including four record closings in five sessions for the S&P 500 prior to Tuesday, the three benchmarks were weighed by technology stocks on the final day of August.

For the S&P, it was a seventh straight month of gains, reflecting the level of investor confidence in U.S. equities derived from the Federal Reserve's continued dovish tone toward tapering its massive stimulus program.

"After all the monetary and fiscal interventions, the question is where do we go from here? Does the S&P go to 5,000, and how does it get there?" said Eric Metz, chief executive officer of SpiderRock Advisors.

While a strong recovery in economic growth and corporate earnings have boosted U.S. stocks in August, investors are concerned about rising coronavirus cases and the path of Fed policy.

A Reuters poll last week showed strategists believe the S&P 500 is likely to end 2021 not far from its current level.

"Where's leadership going to come from, for equities to power higher? Is it earnings growth, is it growth versus value, technology or energy? This needs to be defined, but I think the next leg-up for equities will be sector driven," Metz added.

Technology stocks have continued to garner interest from investors in recent days, given the benefits which lower rates have on their future earnings, although the sector's index was among the worst performers on Tuesday.

Shares of Apple fell after hitting a lifetime high in the previous session, while Zoom Video Communications Inc tumbled as it signaled a faster-than-expected easing in demand for its video-conferencing service after a pandemic-driven boom.

A majority of the 11 major S&P sectors retreated. Among those that did not were the real estate and the communications services indexes, which had earlier in the session hit intraday highs.

Unofficially, the Dow Jones Industrial Average fell 41.42 points, or 0.12%, to 35,358.42, the S&P 500 lost 6.13 points, or 0.14%, to 4,522.66 and the Nasdaq Composite dropped 6.28 points, or 0.04%, to 15,259.61.

(Reporting by Shashank Nayar in Bengaluru and David French in New York; Editing by Aditya Soni and Lisa Shumaker)