MASS Transit Railway passengers caught short in the rush hour may have less to worry about in future as the MTR rethinks its 14-year ban on toilets on the underground. The MTR's deputy operations director, Roger Kynaston, said the MTR could field test automatic toilets - or ''superloos'' - sometime this year. ''In our discussions with the public a number of people asked us to provide toilets, and we are going to look at the arguments again,'' he said. The electronic machines, manufactured by a French firm, are widely used in France and the United Kingdom. People have to pay to use the single cubicles, which flush and clean themselves after use. Ever since it was set up the MTR has firmly refused to put public toilets on its premises. The MTR Ordinance lays down that the corporation is not bound by Public Health Ordinance rules on toilets. Apart from MTR staff, who have their own facilities, anyone who wants to spend a penny has to go to the surface in search of relief. If they do not they could regret it. MTR by-laws state that anyone who allows sewage ''to flow onto or enter or be placed on any part of the railway premises'' faces a $1,000 fine. Mr Kynaston said there seemed little need for toilets on the MTR in 1979. ''The total length of the network was 15 kilometres, so any journey then was short.'' Now the system has more than 40 kms of track. He said there were strong arguments against traditional public toilets. Experience abroad suggested they could act as magnets for all kinds of vice and crime, including drug abuse. They were difficult to keep clean, and it was hard to contain the smell. ''But there are now a number of technological products available which seem to address most of these problems,'' he said.