By Linda Sieg

TOKYO, Dec 1 (Reuters) - A shocked Japan stepped up debate on Monday over whether to send troops to help rebuild Iraq after two of its diplomats were killed there and a poll showed most voters were opposed to the dispatch, at least until security improved.

The diplomats -- who were due to attend a reconstruction conference and were the first Japanese to be killed in Iraq since the U.S.-led invasion -- were among a dozen people from four nations killed in weekend attacks, sparking new concern among Washington's allies about the risks of getting involved.

Japanese media reacted with anger and sadness but were sharply divided over whether Prime Minister Junichiro Koizumi -- who vowed on Sunday not to waver -- should proceed with his plan to dispatch troops.

"Why were these people, who loved Iraq and worked without regard for the danger, killed? The incident is all too painful. Whatever the reason, we cannot forgive the perpetrators," the liberal Asahi Shimbun newspaper said in an editorial.

The Asahi said it was time for Koizumi to admit that conditions in Iraq, which in November suffered the bloodiest month for occupying forces since the U.S. invasion to oust Saddam Hussein in March, did not meet the requirements of a law enacted in July to allow Japan to deploy non-combat troops there.

"More than anything, this is not a situation in which reconstruction activity can be carried out smoothly," the Asahi said. "The guarantee of security for the deployed troops which is required by the law is greatly in question."

Japan has passed a special law to enable it to send troops to Iraq but, in line with the nation's pacifist constitution, they can be sent only to "non-combat zones" to take part in reconstruction and humanitarian work.

DEEPENING DILEMMA

News of the killings has deepened the dilemma for Koizumi, who must balance the demands of vital security ties with the United States with the concerns of domestic voters, who are increasingly nervous about the dangers involved.

The conservative Yomiuri Shimbun newspaper backed Koizumi's tough stance.

"Sadly, that which we feared has come to pass. It is indeed a heart-rending sacrifice," the Yomiuri said. "But we should not flinch. There should be no retreat from Japan's offer of assistance in the reconstruction of postwar Iraq, including the dispatch of Self-Defence Forces (military) personnel."

But it questioned whether security had been lax and wondered why the reconstruction conference that the diplomats were attending was taking place in Tikrit, Saddam Hussein's home town.

"Why was the conference held in that city, of all places? And why did the two head for Tikrit without accompanying security personnel?" the newspaper asked.

Japanese voters, a survey showed, opposed any speedy dispatch but were divided over what the government should do later.

A mere nine percent of voters who responded to a weekend survey by the Mainichi Shimbun newspaper favoured sending troops as soon as possible. Most of the 1,036 who replied to the survey did so before news of the Japanese diplomats' deaths.

Forty-three percent said Japanese troops should not be sent at all, while 40 percent supported a dispatch, but not until the situation in Iraq stabilised.

Support for Koizumi's cabinet, meanwhile, slid to 42 percent, down 14 points from an October survey, the newspaper said, but it did not offer an explanation for the decline.