TAIF, Saudi Arabia (AP) _ Lebanese legislators today debated changing the way their government is structured to provide greater power sharing between warring Moslems and Christians.

The members of the Lebanese parliament are considering ''balancing and overlapping powers'' of a Christian president, a Sunni Moslem premier and a Shiite Moslem parliament speaker, conference sources said.

Conflicts among these Lebanese factions have been feeding the civil war that broke out in April 1975 and has ravaged the nation, claiming the lives of an estimated 150,000 people.

Most recently, Christian leader Gen. Michel Aoun in March sparked six months of lethal shelling when he declared a ''war of liberation'' against the 40,000 Syrian troops in Lebanon, accusing them of siding with the Moslems.

A Arab mediating team made up of Saudi Arabia, Morocco and Algeria, acting on mandate of the 22-member Arab League, arranged a cease-fire Sept. 22 that generally has been holding.

Sixty-three of the 73 surviving members of the parliament have been meeting in this Saudi mountain resort since Saturday to discuss a plan drafted by the Arab League team for ending the sectarian strife. It calls for political reforms and later Syrian withdrawal.

Saudi Foreign Minister Prince Saud al-Faisal steered the deputies away from Christian demands that Syria withdraw before reforms are agreed, to concrentrate on the division of power in the Lebanese government, long dominated by Maronite Christians.

The conference sources said they expected the result to be essentially ''a mechanism of check, recheck and countercheck'' with a view to averting dictatorship or the supremacy of one religious faction over the others.

But the debate indicated a continuing difference of views.

Sources said several deputies rallied behind Maronite Christian leader George Saadeh in advocating that the authority of the powerful president, a Maronite under the present unwritten national accord, be left unchanged.

''It would be hard on us to render our president a mere distributor of medals and decorations,'' Saadeh was quoted as telling the session.

But pro-Syrian Moslem deputy Zaher Khatib told deputies ''we are not in the process of shifting powers from one religious faction to another, we are trying to curtail the powers of a dictatorial ruler and entrust them to a council of leadership (the cabinet of ministers).''

A compromise called for continuing the presidential powers but abolishing the tradition of apportioning senior civil service slots along sectarian lines, now favoring Christians who dominate the military, judiciary and economy.

The deputies met in closed session 10 miles away from the press center where reporters were restricted.

One pro-Syrian deputy, Najah Wakim, unexpectedly showed up at the press center late Monday and said ''opinion gaps among the legislators on the powers of the president have been bridged, the general atmosphere of discussions is favorable, and we are hopeful.''

He refused to elaborate and left the press center abruptly.

Sources said Oct. 21 has been tentatively fixed as the date for a formal session of parliament in Beirut to ratify the new charter that would replace the unwritten accord of 1943.

Two weeks later, the deputies would then meet to elect a new president to replace Amin Gemayel, whose term ran out last September. Parliament was unable to meet to elect a successor and rival administrations sprang up led by Aoun and Moslem Prime Minister Salim Hoss.