(adds more quotes from U.N. officials, details)

By Louis Charbonneau

UNITED NATIONS, April 22 (Reuters) - As many as 300,000 people may have died in the five-year conflict in Darfur, a dramatic increase over earlier estimates of 200,000, a top U.N. official said on Tuesday.

Sudan's U.N. Ambassador Abdalmahmoud Abdalhaleem said the figure was grossly exaggerated and the United Nations cautioned reporters that the number was not a scientific estimate but a "reasonable extrapolation."

John Holmes, U.N. under-secretary-general for humanitarian affairs, mentioned the new estimate in a speech at a U.N. Security Council meeting on the conflict in the western Sudanese region.

"A study in 2006 suggested that 200,000 had lost their lives from the combined effects of the conflict. That figure must be much higher now, perhaps half as much again," Holmes said, according to a written text of his remarks.

Abdalhaleem said Khartoum put the death toll at 10,000, slightly above the government's previous estimate of 9,000. This figure only includes combat deaths because there is no famine and no epidemic in Darfur, he said.

"These remarks by Holmes are not helpful, are not correct, are not credible," Abdalhaleem told Reuters. "He should tell us who made that study, who commissioned it and how was it done."

Holmes was later asked by reporters to clarify his estimate. He said he was "not trying to give an exact figure" and described 300,000 as a "reasonable extrapolation" from the 2006 estimate for the current total number of people who have died in Darfur of disease, hunger or in combat.

Holmes said the original 200,000 figure was based on a 2-year-old study by the World Health Organization. He said there were no plans now for a new scientific study to determine the precise number of deaths in Darfur caused by the conflict.

Asked if the figure could be even higher than 300,000, Holmes said: "I'm trying to be reasonable, conservative."

International experts also say more than 2 million have been driven from their homes by the conflict in Darfur, a region that is roughly the size of France.

DEPLOYMENT DELAY

Holmes described a bleak situation in Darfur, where only 9,000 U.N.-African Union peacekeepers have been deployed out a force that is supposed to number 26,000.

"Darfur today is still characterized by insecurity, lawlessness and impunity," he said.

"Widespread human rights abuses continue to be reported in many areas," he said. "A particularly worrying feature is evidence of high levels of sexual violence."

The joint AU-U.N. special representative for Darfur, Rodolphe Adada, said the peacekeeping force was "very unlikely to achieve full operating capability before 2009," dashing U.N. hopes to have the full force in place by the end of this year.

"Maybe we could achieve 80 percent of the force by the end of this year," Adada told reporters after the meeting.

Abdalhaleem mostly blamed the United Nations for the delay because it had not secured enough helicopters and had not complied with Khartoum's demand that the troops be mostly Africans.

Western diplomats say Khartoum deserves much of the blame for dragging its heels in approving troop contingents.

Holmes said Darfur aid workers also have been victims of violence. He reported 106 hijackings of their vehicles by rebels and their supporters so far this year, a 350 percent increase over 2007, and accused the Sudanese government of not doing enough to protect aid convoys. (Editing by Bill Trott)

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