Defense Minister Yitzhak Rabin suggested for the first time today that Israel is considering accelerating its withdrawal from southern Lebanon in the face of mounting Israeli casualties there.

Speaking to Israeli soldiers at an Army base outside the Lebanese port city of Tyre, Rabin said the Israeli Cabinet may be asked to authorize an early pullout from the predominantly Shiite Moslem areas of southern Lebanon that have been the center of resistance to the Israeli occupation.

Nachman Shai, Rabin's spokesman, who accompanied the defense minister to Lebanon, confirmed tonight that Rabin raised this possibility while talking to the Israeli unit that yesterday stormed the Shiite village of Zrariyeh and killed 34 suspected guerrillas.

"This option is being considered," Shai said of the deliberations within the Israeli Army and Defense Ministry.

Details of the proposal were not known, but it apparently would combine the planned second and third stages of the Israeli withdrawal into a single move back to the border. Such an accelerated schedule could have most Israeli troops out of Lebanon by late spring or early summer, rather than late in the summer as envisaged by the three-stage withdrawal plan that was adopted by the Cabinet in January.

Rabin, who is probably the most influential Israeli government official in terms of policy in Lebanon, may raise the possibility of accelerating the withdrawal in a statement he is to make Wednesday in parliament.

Rabin spoke at the Army base near Tyre as the toll of Israeli casualties continued to mount, with two soldiers killed and seven others wounded in three incidents today.

The two soldiers were killed and two were wounded when an Israeli convoy was ambushed just after it crossed the Litani River along the Lebanese coast and entered the area that Israel evacuated last month in the first stage of its withdrawal.

This afternoon an Israeli soldier was wounded when a car bomb exploded south of Jezzine. Nearby, two hours later, four more Israeli soldiers were wounded by a roadside bomb.

These casualties raised the Israeli toll to 18 killed and 35 wounded since the pullout from Lebanon began on Feb. 16.

Rabin's suggestion that Israel may speed up the withdrawal came a day after various government officials, including Prime Minister Shimon Peres, insisted that Israel would not be forced into a hasty retreat by the increasing wave of attacks by Shiite guerrillas. It appeared to reflect not only the growing domestic pressure to get out of Lebanon as soon as possible, but dismay within the Army at the continuing casualties being suffered in areas that Israel intends to evacuate later in the year.

Rabin has not committed himself to an accelerated withdrawal but appears increasingly inclined to favor it. However, the timing of the withdrawal remains subject to Cabinet approval and any acceleration is likely to be opposed by at least some ministers from the right-wing Likud bloc who argue that a change of plans now would only encourage the guerrillas to continue their attacks up to and across the Israeli border.

Israel completed the first stage of its withdrawal last month by pulling out of the port city of Sidon and the surrounding area. The second stage, planned for sometime this spring, calls for evacuation of Israeli positions in eastern Lebanon near Syrian Army lines.

According to the existing plan, the Israelis would then spend much of the summer on a line that runs from north of Hasbayya, Lebanon, in the east to the present Israeli positions at the mouth of the Litani River along the Lebanese coast, before withdrawing to a "security belt" just north of the Israeli border.

Critics of this plan argue that once warmer weather allows a pullout from the eastern Lebanese mountains there is no point in delaying the final withdrawal to the security belt. They particularly oppose delaying the withdrawal from the Shiite areas east of Tyre that are now not due to be evacuated until the third stage.