UPDATE 1-Heritage offers Ugandan govt tax deal

* Says govt committed to completing deal as soon as possible

* Proposes tax dispute be submitted to arbitration in London

* Offers to deposit $108 mln with Ugandan body in meantime

* Says deal not taxable, in line with past Ugandan oil deals

* Shares fall 3 pct (Adds detail, share price, Ugandan govt comment)

LONDON, June 17 (Reuters) - British oil explorer Heritage Oil (HOIL.L) is hoping to speed up a deal to sell its stakes in two Ugandan oil fields by proposing to put a sum aside to help settle a tax dispute with the Ugandan government.

A landmark $10 billion oil project to develop the East African country's oil reserves, which would see co-owner Tullow Oil (TLW.L) bring in oil majors China's CNOOC (0883.HK) and France's Total (TOTF.PA), is being held up by a tax dispute between Heritage and Kampala.

Heritage said the Ugandan government has assured the company it is committed to completing the transaction as as soon as possible, having concluded its review, and the issue of whether the deal is taxable is all that is outstanding.

Shares in Heritage were down 2.85 percent at 1553 GMT, compared with an index of European oil and gas companies which was 0.5 percent lower .SXEP.

The oil explorer has since January been waiting for formal approval to sell 50 percent of two oil fields on the shores of Lake Albert to Tullow for up to $1.5 billion. [ID:nLDE60G05T]

Heritage on Thursday proposed that the disagreement over tax be referred to binding arbitration in London. In the meantime it offered to deposit $108 million with the Ugandan Revenue Authority once it had received payment from the deal closing.

The FTSE 250 company said should arbitration rule that no tax is payable on the deal, the $108 million would then be refunded to it.

A spokesman in the Ugandan finance ministry told Reuters Uganda had not yet received Heritage's offer.

"I have heard about the press statement but the government of Uganda has not received any official offer or statement in that regard from Heritage and so we cannot comment or consider something we've not seen," said Lawrence Kiiza, Director, Economic Affairs in the Finance Ministry.

Uganda's President Yoweri Museveni told parliament earlier in June that the country would earn around $400 million from Heritage in capital gains tax. [ID:nLDE6511Z3]

The $108 million sum represents 30 percent of the $360 million, equivalent to the 30 percent level of capital gains tax in Uganda, which Heritage says the Ugandan government is seeking.

Heritage argues that no tax is payable on the deal because the government has in the past not taxed previous asset or corporate transactions in Uganda's oil sector.

The proposal to refer the dispute to arbitration in London is in line with the product sharing agreements between the company and the government, Heritage said.

(Reporting by Sarah Young; Additional reporting by Elias Biryabarema in Kampala; Editing by David Cowell)