LONDON (AP) _ The week-old London Daily News evening newspaper is slashing its price in half starting Monday because of what publisher Robert Maxwell called ''sabotage'' by another new evening paper selling at a lower price.

Maxwell also accused rival publisher Lord Rothermere of refusing to supply independent vendors who also carried the Daily News in an attempt to lock out the Daily News from street sales.

The Daily News began publishing a week ago, selling for 20 pence, or 30 cents, on newsstands. The Evening News, a defunct newspaper that was revived on the same day by Rothermere, sells for 15 pence, or 23 cents.

A price slash in half would price the Daily News at 15 cents.

Before the two new evening papers began publishing last Monday, London had only one evening newspaper, Rothermere's Evening Standard, which sells for 20 pence.

The price war is not expected to affect London's other daily newspapers as they are morning papers.

Maxwell said he would allow vendors to keep the 15 cents as an incentive to resist Rothermere's ''intimidation.'' Maxwell claimed Rothermere is refusing to supply the Evening Standard to vendors who carried the Daily News.

''He has sought a price war and he can have it,'' Maxwell said of Rothermere in an interview with Press Association, Britain's domestic news agency. ''It will be an all-out war and it will last for as long as is necessary for the restoration of fair competition.''

Maxwell also said he was prepared to turn the Daily News into a free paper, if need be.

He said his new paper was an outstanding success but did not put a figure on sales.

A spokeswoman said a combined daily total of about 750,000 to 900,000 copies of all editions of the paper had been printed.

Maxwell's decision to give all the cover price to news vendors applies only in London. Vendors outside the area will get to keep four-fifths of the sales proceeds.

Rothermere's Associated Newspapers also publishes the Daily Mail.

Maxwell's Mirror group publishes the Daily Mirror, the Sunday Mirror, the Sunday People, and two Scottish papers.