COLUMBIA, Mo. June 8--For the first time in 29 years, Harry S. Truman won't be coming to this mid-Missouri city for the commencement ceremonies of the University of Missouri, and observers here feel they know the reason why--Truman is going to be in Cambridge, Mass. instead, to get the Harvard honorary degree he has so long desired.

Truman has always considered the Missouri commencement an event not to be missed, one second only to his annual birthday party at the Hotel Muehlbach in Kansas City. Only last week he was again preparing the tribute to Missouri's World War I dead that he has voiced at every M.U. commencement since 1940.

But Saturday a surprise announcement from the office of M.U. chancellor John Schwada said that the 83-year-old ex-President would not be able to come to the June 12 ceremonies because of "a pressing last minute engagement at another college, in the East."

A spokesman for Truman later said that "Harry sure hates to pass up M.U., but, well, he's just wanted this other thing for so long." He refused to elaborate.

The "other thing" is almost certain to be an honorary degree from Harvard which this year holds its Commencement ceremonies on the same day as Missouri University. Ever since his term as President, Truman has been hoping to receive the Harvard degree, but each year his hopes have been in vain. Harvard has passed him over, seeking less controversial and more polished figures.

Give 'em Hell

After this spring's upheaval, however, the University is believed to have changed its mind. By all reports it now feels that it would be entirely appropriate to give a degree to the man who once said (in 1951) "Students? Hell, this country got along without them for 150 years. Why does it need them now?"

The reports of Truman's imminent degree gained further currency late Saturday, when a clerk in the clothing store he owned before going into politics reported that the former President had placed a rush order for a double-breasted, crimson-colored blazer.