* Markets to close Monday, reversing earlier decision * Several companies postpone earnings releases * First weather-related closure in 27 years * Last week, Dow off 1.8 pct, S&P off 1.5 pct, Nasdaq off 0.6 pct * Bond market to open until noon ET NEW YORK, Oct 29 (Reuters) - U.S. stock and options markets will be closed on Monday and possibly Tuesday, the exchange operator said, going back on a plan that would have kept electronic trading going on Monday. As Hurricane Sandy bears down on the New York area, regulators, exchanges and brokers grew increasingly worried about the integrity of markets and the safety of employees. It will be the first time the market has closed for a weather-related event since Hurricane Gloria on Sept. 27, 1985. A number of companies have postponed scheduled earnings releases, including Pfizer Inc and power firm Entergy Corp, and more were expected to follow suit. NYSE Euronext's New York Stock Exchange had initially planned to shut its physical trading floor, which would have meant operating as an all-electronic exchange for the first time. The storm is expected to slam into the U.S. East Coast on Monday night, bringing torrential rain, high wind, severe flooding and power outages. The rare "super storm" - created by an Arctic jet stream wrapping itself around a tropical storm - could be the biggest ever to hit the U.S. mainland, forecasters said. Wall Street had originally prepared to open for business on Monday with limited staffing after a mass transit shutdown in New York, booking hotel rooms for key employees and leaning on offices in other cities. The decision to close stock and options markets came after regulators, exchanges, and dealers discussed the unknowns that would have been tested if the markets opened on Monday, sources familiar with the situation said. The bond market will remain open until noon ET, according to SIFMA, a financial industry trade group. Some bank offices in lower Manhattan's Financial District are in evacuation zones and most non-critical staff and employees who don't rely on high-speed systems, including some investment bankers, were asked to work from home. For a list of how Wall Street firms and exchanges are dealing with Hurricane Sandy, please click On Friday, the Dow Jones industrial average edged up 3.53 points, or 0.03 percent, to close at 13,107.21. The Standard & Poor's 500 Index dipped 1.03 points, or 0.07 percent, to finish at 1,411.94. The Nasdaq Composite Index gained 1.83 points, or 0.06 percent, to end at 2,987.95.