* Slow turnout to register for election worries monitors

* Dispute persists over constituencies

* Threat to boycott poll unless democratic laws are passed

(Adds SPLM comment on slow registration paragraphs 5,6)

By Opheera McDoom

KHARTOUM, Nov 3 (Reuters) - Election observers expressed concern on Tuesday over the harassment of political parties and funding delays as voters began to register for Sudan's first multi-party elections in 24 years.

The Carter Centre, which with the United Nations is providing the only international observers for the vote due next April, said its monitors had faced restrictions and many had not been given accreditation to start their work.

"Sudan's National Election Commission (NEC) must act immediately to accredit national and international observers as well as political party agents, and lift restrictions on observers' freedom of movement," the centre, founded by former U.S. President Jimmy Carter, said in a statement.

Sudanese newspapers have commented on the low turn-out since registration began on Sunday, saying many people did not know that the process had started or where to go to register.

The former southern rebel Sudan People's Liberation Movement (SPLM) said it was concerned there was confusion in registering in the south, and that some centres were not open yet.

"If things go like the way they are going now, I believe less than 10 percent of the total (southern) population will be registered," said senior SPLM official Anne Itto.

Parliamentary, presidential and state-level elections are due in April 2010, followed by a southern referendum on independence in January 2011, both part of a 2005 north-south peace accord that ended two decades of civil war.

Even as the electoral process began on Sunday, doubts remained over whether the election would go ahead beause of a threatened boycott by the SPLM and opposition parties unless a package of democratic laws are passed.

These include bills guiding referendums on secession for the south and the oil-rich Abyei region and on reform of the intelligence services.

The SPLM and the north's dominant National Congress Party (NCP) are also in dispute over the results of a census which should be the basis for electoral constituencies.

"Unless we reach an agreement in the next two or three weeks, it will be very difficult to arrange for the elections," said NCP official Amin Hassan Omer.

U.S. envoy Scott Gration, who has shuttled between the two sides to break the deadlock, said he hoped to see some "positive trends" in the next few days. (Additional reporting by Skye Wheeler in Juba, editing by Tim Pearce)

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