The rulers of the six oil-producing Arab states in the Persian Gulf wound up a three-day summit here today, failing to sign either a collective internal security or defense pact and postponing until next March the implementation of the first steps toward a common market.

They did announce the establishment of a $2.1 billion joint investment corporation that is to back ventures within their own countries and in the West. The six monarchs from Saudi Arabia, Kuwait, the United Arab Emirates, Oman, Qatar and Bahrain were holding the third summit since creation of the Arab Gulf Cooperation Council 18 months ago for the purpose of integrating economies and establishing a pact for collective security and defense.

A communique reaffirmed their intention of building up the strength of their respective military forces to assure the stability and security of the region's Arab regimes but announced no concrete steps.

The six described the recent push of Iranian forces into Iraq as "dangerous" to their security, affirmed support for Iraq's effort to end the war peacefully and called on Iran to respond to Arab, Islamic and U.N. appeals for a negotiated solution.

After more than a year of intensive studies and scores of ministerial meetings, the six have found it more difficult to accomplish their goals than anticipated.

Conference sources said Oman, the poorest, had asked for a delay in implementing measures to abolish tariffs and free the movement of people among the states.