CAIRO (Reuters) - Egypt is to hold a partial legislative vote in June, a first step in a round of elections that will test whether the political establishment will grant opposition groups such as the Muslim Brotherhood more say.

President Hosni Mubarak, who has not said whether he will stand for a sixth term next year, has issued a decree calling elections for 88 members of the Shura Council, essentially an upper house of parliament, said Fathi Ragab, deputy head of the council's constitutional and legislative committee.

The Shura Council reviews laws before handing them to the lower People's Assembly for a final vote.

Nominations for candidates will be accepted from May 5, and the vote will take place on June 1, Ragab said.

Mubarak has the right to appoint 88 members of the council and the remainder are elected, in two blocks of 88 serving overlapping terms.

"All members who have served a six-year term will be replaced ... (Those candidates) must run again or be appointed to a second term," Ragab said.

Most members of the council are affiliated with Mubarak's ruling National Democratic Party or independents.

The Muslim Brotherhood, the non-violent Islamist group that has long been the biggest opposition threat to Mubarak's government, is seeking seats in the council after its members were blocked from running in the last Shura election in 2008.

"Some candidates were even unable to file their applications to run," said Hussein Ibrahim, a member of the People's Assembly affiliated with the Brotherhood.

"This time, we are seeking to gain 17 seats," he said.

Candidates from the Brotherhood will be forced to run as independents, as they do in the lower house, because the group is officially banned.

Egyptians are due to elect a new People's Assembly late this year and to vote in presidential polls in 2011, a possible turning point for the Arab world's most populous nation as it struggles to lift economic growth and modernise.

How the Brotherhood fares in the Shura vote will be a further indication of what to expect in the People's Assembly. Politicians linked to the group now control a fifth of seats there, by far the biggest opposition bloc.

"The possibility of the Brotherhood winning or losing (in the Shura race) is highly dependent on the security forces and ... how they confront them," said Nabil Abdel Fatah, from the Al-Ahram Centre for Political and Strategic Studies.

Over the last few months security forces have detained dozens of members of the Brotherhood, which says it wants to set up a democratic Islamic state by peaceful means.