A father-son difference of opinion between House Majority Leader Thomas P. O'Neill (D-Mass.) and Lieut. Gov. Thomas O'Neill Jr. has arisen over the endorsement of presidential candidates, although both have said that this will not cause a family conflict.

O'Neill Jr. has endorsed Democratic hopeful Sen. Birch Bayh (D-Ind.), while his father has publicly supported and campaigned for Rep. Morris K. Udall (D-Ariz.).

The elder O'Neill said one of the major reasons for his choice for president was that after working with Udall in the House for the past 16 years, he felt the Arizona congressman "towers over the other candidates intellectually and every other way."

When asked about the effect that this rift in opinion between him and his son might have on their relationship, O'Neill replied, "He (Lieut. Gov. O'Neill) is going his street about this, and I'm going mine. I haven't seen him lately and I don't know how his candidate is doing, but I think mine is going to win."

The younger O'Neill brought up reasons similar to his father's for endorsing Bayh. He said that after having had the opportunity to speak with all of the competitors, he thought that Bayh was "head and shoulders above the other candidates." O'Neill Jr. mentioned Bayh's impressive record in the Senate and his help in drafting the 25th and 26th Amendments as proof of the contender's worth.

The lieutenant governor said that he had decided to support Bayh almost four months ago and had discussed this with his father then. The elder O'Neill told him that he hadn't made up his own mind yet about the candidates, but he wanted his son "to do what he wanted."

Lieut. Gov. O'Neill added, "My father is comfortable with Mo Udall and I'm comfortable with Bayh. I'd hate to think this would cause a family rift...but it won't. We're that close."