United Nations considers new role for its secretary-general

The United Nations has set out to strengthen its peacekeeping role.

It wants to overcome its impotence and avoid the fate similar to that of the League of Nations (which eventually dissolved as major powers decided to quit it or to ignore it).

The UN General Assembly now is expected to pass a resolution by consensus, which would in effect give the position of the UN secretary-general a stronger hand in exerting ''preventive diplomacy,'' according to Javier Perez de Cuellar, the current secretary-general. Mr. de Cuellar recently published a report that:

* Described the growing irrelevance of the UN as member states refuse to abide by its decisions and the ensuing threat to the very fabric of international peace.

* Suggested ways in which the secretary-general could play a more forthright role in averting war (particularly by warning the Security Council of potentially dangerous situations and by sending fact-finding missions to potential conflict areas).

He did not propose to modify the UN Charter but wanted a more vigorous behind-the-scenes role in search of peaceful settlements.

Basically, what the secretary-general has in mind is a gradual reform by the Security Council of its working habits. The resolution lends the secretary-general strong moral support while not expanding the General Assembly's role at the expense of the Security Council, according to informed sources.