(adds comment from prime minister's spokeswoman)

LONDON, Feb 21 (Reuters) - An early draft of a pre-war British weapons dossier on Iraq included concerns over Israel's nuclear capability, but the government fought to suppress the reference before publication, The Guardian reported on Thursday.

The newspaper said the Foreign Office convinced a tribunal to keep secret the handwritten mention of Israel in the margin of the dossier, which was drawn up to justify going to war in Iraq.

The reference, suggesting Israel had disregarded the will of the United Nations like Iraqi leader Saddam Hussein in pursuit of weapons of mass destruction, was removed before the draft was released this week under Britain's Freedom of Information Act.

Israel, seen as a key British government ally, is thought to have the Middle East's only atomic arsenal.

In a witness statement to the Information Tribunal, seen by The Guardian, a senior Foreign and Commonwealth Office (FCO) official warned that any candid reference to Israel would seriously damage bilateral relations.

"I interpret this note to indicate that the person who wrote it believes that Israel has flouted the United Nations' authority in a manner similar to that of the Iraqi regime of Saddam Hussein," the official said, according to The Guardian.

"Unfortunately, there is a perception already in Israel that parts of the FCO are prejudiced against the country," Foreign Office official Neil Wigan was quoted as saying.

He argued that the reference scrawled on the draft dossier "would therefore confirm this pre-existing suspicion and would increase the damage".

Asked about the Guardian report, a Foreign Office spokeswoman told Reuters: "We don't comment on leaked documents."

A spokeswoman for Prime Minister Gordon Brown would not comment on the document itself but said: "Our position in terms of encouraging all signatories of the (nuclear) non-proliferation treaty to abide by that remains the same."

"But we also recognise Israel's position needs to be looked at in a regional context, bearing in mind they have neighbours such as Iran who deny the right of Israel to exist."

Succumbing to three years of pressure from freedom of information campaigners, the British government released the once-secret draft document on Monday.

The 32-page dossier, written by a former director of communications at the Foreign Office, cites intelligence sources saying Iraq had stockpiles of chemical and biological weapons and could easily use them since it had done so before.

The document, amended in the margins, makes no mention of Iraq being capable of launching weapons of mass destruction within 45 minutes, a false claim later used in another government dossier to make the case for going to war. (Reporting by Paul Majendie and Katherine Baldwin; Editing by Andrew Hough and Caroline Drees)

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