ACCRA, April 4 (Reuters) - Northern members of Ghana's ruling National Democratic Congress (NDC) want to ensure the party's candidate for vice-president comes from the region, whose ethnic groups say they have been sidelined.

The party is due to hold its national congress at the end of April with Ghana's current vice-president, John Atta-Mills, a southern Fante, widely tipped to emerge as its candidate for the December election which will choose a successor to President Jerry Rawlings.

Rawlings, president since 1981, is standing down at the end of his constitutionally allotted mandate.

"The main criteria should be capability first, and then regional balance; and we think we have many capable men and women," a senior government minister from the north told Reuters privately.

Party officials say that Attorney-General and back-room party tactician, Obed Asamoah, who is from Rawlings' minority Ewe ethnic group in the eastern Volta Region, has been lobbying for the vice-presidential nomination.

Rawlings, who is coming to the end of two consecutive four-year terms, is ineligible to run under the constitution agreed after Ghana's return to constitutional democracy in 1992.

Both vice-presidents under Rawlings have been from the majority Akan ethnic group.

"Our argument is that since it has been an Ewe-Akan leadership team since 1992 up until now, it should not be Ewe-Akan again," Alhaji Salpawuni Alhassan, a senior party official in Tamale, capital of the Northern Region, told the independent Ghanaian Chronicle newspaper.

"If we don't get on the ticket now, the same team will run again in 2004 for another four years; we can't wait that long," he added.

Northern Ghana grows much of the former British colony's grain but is the least developed part of the country. Political sources say that northerners hope to reverse that trend by getting closer to the centre of power.

Last week, NDC youths in Tamale staged street demonstrations against Asamoah, whom many in the party regard as aloof and arrogant.

The northern lobby wants the soft-spoken deputy education minister, Mohammed ibn Chambas, 47, or Alhaji Mahama Iddrissu, presidential advisor on governmental affairs, who is in his early sixties, to run with Atta-Mills.