Securities industry officials, convinced that a merger of the New York and American Stock Exchanges is at best a pipedream, today urged the two exchanges to look for ways to share facilities in new areas such as futures and commodities trading.

The executive board of the Securities Industry Association voted to form a "blue ribbon" group to act as an "honest broker" to facilitate cooperation between the Amex and the NYSE.

The securities group, the largest of the Wall Street trade associations, wants the two exchanges to jointly operate facilities to save them money. If both the Amex and the NYSE operate their own trading floors for commodities and futures contracts, brokers would have to maintain separate operations for each.

The trade group had called for a merger of the two exchanges in 1974, but concluded today that the reluctance of Big Board members to merge as well as antitrust considerations, preclude establishing one big Wall Street stock exchange.

However, according to SIA chairman Willard S. Boothby Jr., since the Amex is planning to build a new facility (with New York state aid) and the Big Board is planning to open either a new trading floor or an entirely new location, both should consider either sharing some facilities or locating next door to one another.

The Amex already has started pilot trading in futures contracts, limited now to a single Government National Mortgage Association Security.The NYSE has said it will start up a futures trading exchange of its own and will lease new trading space for that facility.

The Amex has been trading its stock options (which give the purchaser the right to buy stock in a specific company at a specific price at some future date) for several years and the NYSE also plans to venture into the options trading field.

In another development, the securities association said it would provide $125,000 to set up a new "shareholders" lobby that would push for tax changes favorable to investors.

The SIA said the plans are for member brokers to mail solicitations for a fledgling Investors For Tax Equity to about six million of their customers, hoping that about 1.1 percent (66,000) would pay the $15 a year membership fee. The new group would then repay the $125,000 "loan" from the membership fees.

Last year, the SIA put aside $100,000 seed money for such a group, but could interest no other big associations in contributing to it.