London — The days of that most Britannic of institutions - the royal blue passport with covers as stiff as a British upper lip - are numbered. In three years it will be replaced by a travel document designed in Brussels.
As a member of the European Community, Britain is bound to accept a policy stating that all citizens of the EC should have passports that look more or less the same.
But by insisting that from 1987 Britons must tumble into line, Home Secretary Leon Brittan has touched a chauvinist nerve.
For the British passport enjoys a special aura. There is the lion and unicorn emblem on its cover, with its twin mottoes: ''Honi soit qui mal y pense'' and ''Dieu et mon droit.''
There is also the bombastic phrasing inside the cover: ''Her Britannic Majesty's principal secretary of state requests and requires etc.''
And there is the blueness, the sheer physical substance of the document.
All combine (or so it is thought) to make the British passport a palpable and puissant companion when venturing abroad.
EC officials, being bureaucrats, do not see it that way. A passport to them should be a symbol of European unity.
So they have decreed that it will be somewhere between brown and red in color and that the words ''European Community'' must appear on its cover.
For no apparent reason, the bureaucrats also want a passport with limp covers - a detail that Britons might accept with equanimity were it not for one other feature. The new EC passports will include a strip of plastic containing information about the bearer and designed to be run through a computer at ports of entry.
The little bit of plastic is agitating Britain's civil righters. They fear it will be used to store unfavorable facts about citizens.
Their concern is rather more than eccentric. Britons have always resisted identity documents of the type common in Europe. Opponents of the new passport argue that it resembles an identity card, complete with computerized features.
Mr. Brittan has tried to defuse the Euro-passport issue.
The new document will still have ''United Kingdom of Great Britain and Northern Ireland'' written on it.
The lion and unicorn emblem (a trifle shrunken) will still appear on the cover. But it will be a smaller passport, and the regal blue will be no more.
And because it will be soft covered, the irate British traveller will not even be able, as the London Times observed, to use its sharp edges and corners to fight off alien hordes.