Agriculture Minister Ariel Sharon's plan to step up rapidly the establishment of Jewish settlements in occupied Arab territories appears impractical and has little support with Prime Minister Menahem Begin's government, in the view of observers here.

Informed sources say there is little likelihood that the government would endorse Sharon's proposal that 2 million Jews be settled in the West Bank, Gaza Strip and Golan Heights by the turn of the century.

Sharon, the cabinet minister responsible for planning the establishment of Israeli settlements in territories seized during the 1967 war, has presented his proposals to Begin and other members of the cabinet but, according to informed sources, there has been no discussion of them.

In addition, the sources point out, the proposals have not been examined by any of the groups of experts that deal with new settlements nor by the joint settlement committee of the Israeli government and the Zionist movement, even though Sharon heads the committee.

The plan is expected to encounter opposition even from the extremist group, Gush Emunim, which last week reiterated its intention to establish 12 settlements in the occupied territories "by the end of the summer." Hinting that a clash with Gush Emunim was possible, Sharon said that no settlement will be allowed without the government's approval and if Gush Emunim acts indenpendently "the government will have to decide."

While there have been no official reactions to publication this week of the Sharon plan, there are signs that some ministers are displeased. Especially resentful is said to be Foreign Minister Moshe Dayan, who is now putting the final touches on his own solution for the West Bank problem. He expects to present it during talks he will have in Washington and New York with President Carter and members of his administration and with other foreign ministers attending the United Nations General Assembly.

Although he insists on the right of Jews to settle anywhere on the West Bank, Dayan has stressed that only places where there is government-owned land or where Arabs have sold out to Israelis should be settled. The Sharon plan makes no such stipulations.

Sharon, who won fame as one of Israel's outstanding generals on the battlefield and led the Israeli forces which crossed the Suez Canal into Egypt during the 1973 war, has done little in politics until now. In the general elections in May he ran on his own tickets, which won only two seats, and he later joined the victoriuns Likud Party.

He unveiled his plan openly last week in a lecture in the Golan Heights and subsequently presented in an interview on Israeli television Friday night and in an English Language radio broadcast on Saturday. According to his plan, Israeli urban and agricultural settlements would be strung along two parallel lines in West Bank areas where the Arab population is relatively sparse. One of these lines would be the Jordan River in the Jordan Valley, where 20 Israeli settlements have been established since 1967. The other, north-south line would be west of the watershed that runs from Nablus to Hebron. There would also be two west-to-east lines of settlements cutting through the West Bank - one south of Nablus in Samaria and the other in the Jerusalem area.

The Sharon plan includes some of the elements which guided the outgoing Labor Government as it established settlements between 1967 and 1977, but experts point to two basic differences: publicity and scale. While previous governments believed action should precede words mainly so that both friend and foe would be antagonized as little as possible. Sharon telegraphs his moves in advance regardless of political consequences.

Until now no more than 8,500 Israelis are living in settlements established since 1967. But Sharon talks of two millions occupying areas from the Golan Heights to Shar-El-Sheikh - a figure which most Israelis believe to be totally unrealistic.

Yet the Sharon plan provides that no setttlements should be established in areas where there is a dense Arab population. This is contrary to the ideas of Gush Emunim activists who believe that Israelis must settle the heartland of Judea and Samaria, including the main towns which have played important roles in Jewish history.

To questions of why Prime Minister Begin, who keeps strict controls over the utterances of members of his cabinet, allowed apparently premature publication of the Sharon plan, observers give three possible answers.

These are:

The Begin government sees a need to forestall the action of Gush Emunim and other supporters who feel it is not acting fast enough, and to convince them that it is not holding up the settlement effort.

The Sharon plan is a "trial baloon" to measure reaction both in Israel and abroad.