Although the "Mock Republican Convention" sponsored by the Law School Forum at Lowell Lecture Hall last night left Richard M. Nixon and Nelson A. Rockefeller still even in their race for the G.O.P. nomination, speakers Al Capp and Walt Kelly established one thing, at least. The opposition candidate, "from the American political gutter," should be Harold E. Stassen they agreed; "if Harold can do it in blackface, he might make out."

Kelly took this viewpoint, after admitting that he "had not considered the possibility of there being an opponent." Earlier, he defended Rockefeller against the attacks of Capp, a Nixon supporter.

The evening's opening speaker, Kelly, began, "Here in the menopause of our national history ... I seem to have Mr. Capp's speech." As he brandished a sheaf of documents, he intoned, "I hold here in my hand 205 references ..."

Getting down to business, he pointed out that Rockefeller's father had given his children a bicycle to share, but that "one man (Nelson) wound up with all the wheels. It is this sort of luck and gimleteyed perspicacity that marks a man suited for the Presidency."

Quickly battling back, Capp proclaimed, "It is true that the elder Rockefeller did the equivalent of giving everybody in America a dollar. But Mr. Nixon has given us something twice as valuable--Richard M. Nixon." He said his announcement of Nixon's candidacy would come as a shock to the vice-President, who "has been all over the country" trying to do his present job.

Capp spoke of Nixon's television appearance during the 1952 campaign, when the candidate refuted charges that "well-heeled California patriots had been slipping this boy $18,000 a year." Concluding, he said, "The great and compelling reason to put Nixon in the White House is that we can keep our eyes upon him."