Prime Minister Benjamin Netanyahu has offered to have some members of the right-wing National Union Party join his coalition and the cabinet.

The proposed move comes shortly before the prime minister is expected to deliver a major diplomatic policy speech in the United States in May or even earlier, either to a joint session of Congress or at the convention of the pro-Israel lobby AIPAC, the American Israel Public Affairs Committee.

Netanyahu has been engaged in talks recently with National Union faction chief Yaakov Katz over the prospect of Katz joining the coalition along with party colleagues Uri Ariel and perhaps Aryeh Eldad.

The prime minister did not ask the National Union's fourth MK, Michael Ben Ari, who is identified with the late Meir Kahane's extremist Kach movement, to join the coalition.

At this time, the discussions have run aground because the prime minister has refused Katz's demand that Netanyahu publicly declare an intention to carry out large-scale building in Jerusalem and in the West Bank settlement of Ma'aleh Adumim just outside the city.

In the course of the talks, there was discussion of Katz being appointed a cabinet portfolio, either as social affairs minister or as minister for the development of the Negev and Galilee.

The social affairs portfolio is temporarily being filled by Communications Minister Moshe Kahlon, while Vice Prime Minister Silvan Shalom is serving as minister for the development of the Negev and Galilee.

A source close to the prime minister said no agreement had yet been struck with the members of the National Union because "Netanyahu is a man of principles."

Nonetheless the effort has been met with surprise in the political establishment in light of the prime minister's intention to announce a far-reaching diplomatic initiative while in the United States, to include the transfer of additional West Bank territory to the Palestinian Authority's control.

The overture to National Union MKs is seen as a reflection of Netanyahu's view that there is no chance of having Kadima or a portion of the centrist faction join the coalition.