WASHINGTON (Reuters) - A postponement may be in the works for approaching deadlines to implement new U.S. Securities and Exchange Commission rules on stock market pricing and trading, SEC officials said on Saturday.

"We think it's fair to ask whether the existing deadlines remain realistic," said David Shillman, a senior official in the SEC's Market Regulation Division during a panel discussion at the annual SEC Speaks conference in Washington.

"The staff is discussing it internally. I would expect the commission to decide in the near-term if an extension is warranted and if so, for how long," Shillman said.

The SEC voted in April 2005 to adopt Regulation National Market System (Reg NMS), a far-reaching set of pricing and trading reforms. The vote came amid intense debate over its most complex section, the order protection rule.

As adopted, the rule bars traders from ignoring the best price for a stock when executing a buy or sell order, as long as the price is available on a fast, automated market.

If the best quoted price is only available on a so-called slow market, like the manual New York Stock Exchange trading floor, then it may be bypassed.

The order protection rule is pressuring the NYSE to shift trading onto automated systems. This is occurring in the midst of implementing other new rules and as the NYSE and the Nasdaq Stock Market work to complete major acquisitions.

Brokerages affected by Reg NMS have been pleading for more time to work with new trading systems before the order protection rule takes full effect.

At present, the compliance date for 250 large stocks is June 29, with other stocks expected to comply by August 31.

The changes mean securities markets have a large workload to reconfigure trading and surveillance systems. That has raised questions about whether the SEC may delay the implementation of the order protection rule.

"There's a lot of concern about the amount of data that firms would have to retain in order to comply," Shillman said.

Robert Colby, acting director of the Market Regulation unit of the SEC, said the full five-member commission would likely have to act on any postponement of NMS implementation.

Other aspects of Reg NMS -- such as a ban on sub-penny price quotes -- are being implemented on schedule.