London — If genius can justifiably be described as an infinite capacity for taking great pains, then those Victorian painters known as the Pre-Raphaelites must have been geniuses to a man. Was there ever a kind of painting that made such a virtue of painstaking detail? Which assumed, as though it were an end in itself, that literal accuracy was a scrupulous necessity?
A large-scale look at the Pre-Raphaelites - most significantly at its best-known painters, Rossetti, Hunt, Millais, Brown, and Burne-Jones - is being taken by the Tate Gallery through May 28. It is the most popular exhibition at the Tate since the gallery's Dali show four years ago. Two or three thousand visitors a day are coming to see such paintings as Hunt's ''The Light of the World'' and ''The Scapegoat''; Millais's ''Christ in the Carpenter's Shop'' and ''The Black Bruns-wicker''; Rossetti's ''Ecce Ancilla Domini!'' and ''Beata Beatrix''; and Brown's ''The Last of England'' and ''Work.''
Possibly the popularity of such pictures is due to the persistent (and peculiarly British) belief that the criterion for any artist's artisthood is his ability to reproduce the minutest surface facts, the recognizable appearance, of the physical world. In this aspect the Pre-Raphaelites, or the Pre-Raphaelite Brotherhood, as they called themselves, owed much to the advice of Ruskin. This all-important critic of the day wrote that ''the young artists of England'' should ''go to nature in all singleness of heart, and walk with her laboriously and trustingly, having no other thought but how best to penetrate her meaning: rejecting nothing, selecting nothing, and scorning nothing.''
It would be hard to codify an aesthetic more alien than this to a free play of imagination, or quickness of perception and inspiration. Coming out in support of the youthful and beleaguered ''PRB'' (with which they esoterically initialed their first pictures), Ruskin insisted that they had followed his advice ''to the very letter.''
To the 20th century, these sonorous aims of Ruskin summarize everything rejected by the most radical forms of modern art: They run counter to the release of the subconscious as a motivating force and they oppose freedom from slavish representation - a freedom that has led to the most far-reaching forms of so-called abstract art.
Currently we are supposed to be in a post-modernist phase. Perhaps the extraordinary concentration of Victorian awfulness in an exhibition like ''The Pre-Raphaelites'' will return us decisively to an exploration of our own century's sensibility. With Ruskin's cramping dictum, is it any wonder that most of the Pre-Raphaelites found the meaning of life to be a matter of maudlin or morbid frustration?
The exhibition, which must be praised for its ''scorning nothing'' approach to one of art history's odder aberrations, extends from the founding of the brotherhood in 1848 to the death of Rossetti in 1882. A difference between critics and historians is that a certain impartiality of taste seems (never more so than today) required of the historian. The organizers of this exhibition aim at this kind of suspension of judgment in their attempt to present the PRB in the fairest light. In this way, the Tate's director, Alan Bowness, who wrote the show's catalog introduction, finds that ''ultimately it is the sheer variety of the work produced (by the Pre-Raphaelites) that impresses.''
This last question is not easy to answer because English painters do not often form themselves into groups - and even the PRB soon split up, each member following a highly individual course.
As for the variety of their work, the exhibition itself, in spite of the marked characteristics of the artists included, still adds up to a strangely repetitive endeavor. Though every one must have been earnest - and none more so than Holman Hunt in his religious pictures - one finds himself calling into question their very sincerity as painters. Perhaps they were simply trapped by the prevailing atmosphere. But they could slip so easily into the confusion of unselected detail, into naive (''trusting'') sentimentality, and above all into an overambitious effort to somehow contain the heights and depths of religious experience within the sterile literalism of exhaustive objectivity.
To explain the newness of their ideas and style, the argument goes that English art had sunk to a nadir by the middle of the 19th century. But what did they really offer as a rescuing, revitalizing force? It could be sadly argued that their advent took English painting to even more dismal depths. They were influential, certainly. Their dead-bright colors and their sentiment became the order of the day rather than the older generation's dark colors - and sentiment. Their history painting was still history painting even if it did look at different periods. But their so-called return to the purer, more truthful world of the Italian primitives before Raphael seems to have been based on a large (though understandable) ignorance. Prints after the Campo Santo frescoes in Pisa by Bennozzo Gozzoli and Van Eyck's ''Arnolfini Marriage'' were among the few pre-Raphael works they seem sure to have seen - though Rossetti did travel on the Continent in October 1849 and must have seen some other early paintings then.
Madox Brown, though never a precise member of the brotherhood, was definitely affected by his contract in Rome during 1845-46 with the group of German artists called the Nazarener, whose aim was to paint religious works in the style of the early Renaissance artists. But, oddly, Brown remained the only artist associated with the PRB who seems to have recognized that poetic and religious underpinning does not, just on account of its sincerity, guarantee good art. Complaining that people tried to read too much symbolism into one of his paintings, he said: ''In all cases pictures must be judged first as pictures - a deep philosophical intention will not make a fine picture.'' As a Pre-Raphaelite remark it is like a breath of fresh air - compared, say, with this by Millais on his projected painting ''The Eve of the Deluge:'' It was, he said, ''to affect those who may look upon it with the awful uncertainty of life and the necessity of always being prepared for death.''
But even Brown - who of all of them was capable (on occasion) of straightforward painting - relished the crowded, labored composition, the drowning of imagination with literal-mindedness and ''historical accuracy.''