Prime ministerial aides were more flustered today than at any time since the 1968 election when black-hatted John Lennon and Yoko Ono called on Prime Minister Trudeau.

One reporter was selected by Press Secretary Romeo Leblanc to be permitted into the presence of the English Beatle and his wife with Mr. Trudeau.

But Mr. Leblanc’s assistant, Vic Chapman, a former professional football player, would not let the reporter in. Television cameramen and photographers were permitted entry.

Three plainclothes security guards were on hand as well as the usual Commons protective staff.

Marc Lalonde, principal secretary to the prime minister, and Gordon Robertson, clerk of the privy council, cut short a conference with Mr. Trudeau and left his office just before the long-robed visitors arrived.

Mr. Lennon had twice asked for an audience with Mr. Trudeau and made it on the second .attempt. He arrived here at 2 a.m. to prepare for the 11 a.m. meeting, which lasted some 30 minutes.