Some 200 University Research Fellows may lose sizeable chunks of their incomes as a result of a recent ruling by the Treasury Department, it was learned yesterday.

Up until now, University grants for pure research, like scholarships, have been tax-exempt. Now, however, those Research Fellows whom the Treasury thinks have completed their training and are already embarked on careers will have to pay taxes on their stipends.

No Specific Rule

According to John M. Maguire, Royall Professor of Law, the new ruling would be likely to affect numerous doctors who receive grants for such projects as cancer research.

He pointed out, however, that the Treasury provides no easy rule of thumb and that each individual case would probably be reviewed separately to determine its tax status. "Right now it is impossible to make general predictions," he explained.

Other officials declined to comment on possible University action but indicated that they were "concerned" with the problem. Earlier this year the treasury Department ruled that Fulbright scholar ships were taxable but later reversed itself after considering evidence offered by the State Department.

Section Men Taxed

Unlike section men, who receive taxable salaries for their teaching duties. Research Fellows perform no specific services for the University. The latter have generally been regarded as post graduate students-in-training preparing for careers in research.

Under the new ruling, however, men who engage in research projects which are not solely for their own training or education but could conceivably benefit society at large might be subject to taxation.

The Treasury first began distinguishing between "professional" and "student" holders of fellowships in 1949, but so far the majority of Research Fellows here have remained tax-exempt.