The people of Israel must have mixed emotions in the wake of Prime Minister Menachem Begin's decision to resign. They are, on the one hand, losing a leader of uncommon courage and determination. From the time that he headed the Irgun, the underground terrorist organization, Mr. Begin has been single-minded in his Zionist aims: first to establish an independent state of Israel and then to help extend its sovereignty over the historical lands of Judea and Samaria. Mr. Begin will leave office knowing he has brought his vision of ''Eretz Israel'' closer to reality.
But is the Begin vision the right one for the Jewish people? Will it give them the secure homeland they seek? Even as many Israelis admire Mr. Begin's political daring - making peace with Egypt, for instance - they must wonder whether his achievements have brought Israel closer to peace or nourished the ground for continuing conflict.
Certainly the cost of his policies has been high. As a result of Israel's lunge into Lebanon, hundreds of Israeli lives have been lost. Casualties continue to mount as Israeli forces prepare for an indefinite stay - occupying still another territory belonging under international law to someone else. Add to this Israel's loss of moral stature in the eyes of the world as a result of its indirect role in the massacres at the Sabra and Shatila camps.
The unrelenting drive to absorb the occupied West Bank is of dubious blessing even in militant Zionist terms. Israel may be providing more living space for Jewish immigrants. It may be feeding the pride and ambitions of those who envision a ''Greater Israel.'' But it is also creating a state that embraces some 2 million Palestinians and that will necessarily change in character as a result. Israeli democracy can only be undermined by the establishment of two separate systems of justice and administration. And Israel's security problems threaten to grow as a result of hostility from such a huge Arab population and the need for tighter military control.
Economically, Israel is in a precarious state. It has an external debt of $ 26 billion and is dependent on continuing massive infusions of United States aid to sustain itself. Can Israel count indefinitely on American generosity to keep itself afloat as it pursues its territorial aims? Especially now that US Marines have been killed in Lebanon and the American people begin to feel the personal cost of ''peacekeeping'' in the Middle East?
The Israeli people, in short, have much to ponder. In the near term, Israelis will focus their attention on the scramble to form a new coalition government. Mr. Begin's departure, prompted largely by personal considerations, will doubtless leave a void in strong leadership. His commanding authority and presence are likely to be missed even by those who criticize his policies. But beyond the immediate political uncertainties lie the larger persisting questions of Israel's future.
Can the nation endure under a policy which denies to others the right of self-determination it demands for itself? Does true security reside in the tangible possession of land, or in those intangible moral and spiritual qualities of respect and love for neighbors that make for genuine peace? Can Israel ever end its own sense of beleagueredness until it reaches out with sympathy to others burdened with their own feelings of frustration and injustice?
Menachem Begin's response has been a defiant policy of aggrandizement. As Israelis weigh the heavy price of the Begin legacy, it can be hoped they will begin demanding different answers.