So far, rather few service jobs have been ‘‘offshored.’’ There are call centers that handle airline bookings, technical teams that talk computer buyers through their frustrations, and a few experiments in providing legal and accounting services over fiber-optic lines. But the bulk of trade still consists of manufactured goods and farm products — things that can be packed into boxes and loaded onto cargo ships.(A recent Post story on outsourced maths tutions suggests) This is going to change over the next decade or so. If a teen-ager in Potomac, Maryland, can learn geometry from a tutor in Cochin, India, there’s no reason why many other U.S. service jobs can’t be done from abroad.How many? Well, so far fewer than 1 million U.S. service jobs have been moved out of the country, a small number given that the U.S. labour market routinely destroys and creates more jobs than that every two weeks. Forrester Research has estimated that the total could rise to 3.3 million by 2015; consultants at McKinsey have suggested that 13 million jobs are at risk of moving offshore. But an alarmingly plausible analysis by Alan S. Blinder of Princeton University. estimates that as many as 42 million U.S. jobs are potentially at risk. That’s almost a third of all jobs in the economy. It’s also three times more jobs than exist in U.S. manufacturing.But the case for trade in services is as sound as the case for trade in manufactures. Yes, there are losers: in this case, American math tutors. But there is a more-than-offsetting benefit to American consumers, and notably to Americans with modest incomes. The availability of $20-an-hour math tutoring may help erode the advantage that rich children have in college entrance tests. Meanwhile, foreign exporters get a chance to escape poverty; the tutor in the Post story was earning twice as much as in her previous job as a high school teacher. And the idea that any of this erodes American vitality is unconvincing. To the contrary, Indian math tutors may boost U.S. high school math scores, fixing a much lamented weak spot in the nation’s competitive outlook.(An editorial in The Washington Post on May 17)