Scotland's national galleries are in a race against time to raise the final £750,000 required to save one of the country's most famous images, Landseer's The Monarch of the Glen, for the nation.

The National Galleries of Scotland (NGS) have secured £3.25m towards the £4m price agreed with its owners, the drinks giant Diageo, but are now asking the public to help contribute to the cost of purchasing the art work.

If the deadline is reached without raising the required money, the painting will likely be sold on the open market by Diageo, who had already planned to sell it at auction before it entered talks with the NGS last year..

The price of £4m, Sir John Leighton, director general of the NGS, is half of the lowest price (£8m) its own evaluators judged the painting to be worth on the open market - other estimates received for the galleries said it could be sold for more than £15m at auction.

The agreement to give the galleries a period of time to raise £4m was reached between the institution and Diageo in November last year.

The painting of the stag, created in 1851 by Sir Edwin Landseer, may justify the over-used description of 'iconic', being recognised as a symbol of one aspect of Scotland the world over through its many iterations in marketing for drinks and food.

The artwork is currently not in Scotland and may not be again if it is sold at auction.

The Heritage Lottery Fund (HLF) has agreed to support the campaign with a donation of £2.75m and the Art Fund has also gifted £350,000.

Along with other donations and pledges, this means that the NGS has already raised £3.25m towards the final target.

Sir John said: "We are still in discussions with trusts and foundations, but donations from the public can help across a wide range, whether they are small amounts or not, and that sort of support encourages other people - so every little helps, it's a cliche but its true.

"So far we have had a lot of unsolicited donations from as far away as Alaska, from Europe, from America, but my experience is that people really respond very warmly to this painting.

"I am pretty optimistic but I am not complacent either, it is still quite a lot of money to raise."

People can donate online, send a cheque to the galleries, or buy a £10 Monarch of the Glen lapel badge at the galleries, he said.

Sir Peter Blake has contributed a video supporting the cause - he once painted a version of the Monarch of the Glen for Sir Paul McCartney. In the video he said the "magnificent" painting deserves to stay in Scotland.

The painting has been a key loan to two important exhibitions organised by the National Galleries of Scotland: The Discovery of Scotland (1978) and The Monarch of the Glen: Landseer in the Highlands (2005).

Sir John added: "The painting is currently not in Scotland, and of course that is dearly what we would like to do in March, bring it back in a triumphant return.

"It was already on its way to auction when this opportunity intervened, so whether they [Diageo] sell it immediately, or hang on to it and sell it, they have made it pretty clear that it is does not have a home in their ownership.

"If it doesn't work, I would have hoped that we have given it our very best effort, but I would be supremely disappointed but it is such a fantastic opportunity."

Sir John said in commercial terms the £4m price is an "extremely good deal, and we will never get a better chance at it".

"Can you think of many other pictures, from the realms of fine art that have become absorbed into popular culture and become so ubiquitous and so famous in so many contexts?" he said.

"Yes, Van Gogh's Sunflowers and the Mona Lisa, but this has to be one of the most familiar images in the world and the bottom line is, it's an absolutely stunning picture."

Ros Kerslake, chief executive of the HLF said: “The Monarch of the Glen is an evocative painting which has earned global recognition. "With the help of National Lottery players, we are playing our part in securing it a permanent home at the National Galleries of Scotland. "We very much hope the fundraising campaign will be successful and enable many more people to enjoy this beautiful and historic painting."

Dr. Stephen Deuchar, director of the Art Fund said: “This technically superb picture is as interesting and provocative today as it was when first exhibited. I hope the public will support the NGS's campaign."

Fiona Hyslop, the culture secretary, said: “I congratulate the National Galleries of Scotland on securing significant sums from the Heritage Lottery Fund and Art Fund to support their acquisition of the iconic Monarch of the Glen painting.

"I wish them every success with their campaign to raise the remaining funding to ensure the painting can remain in public display in Scotland so that visitors from across Scotland and around the world can continue to enjoy it."