The top two officials of the congressional Joint Committee on Taxation announced yesterday that they plan to leave by the end of the year.

Bob Shapiro, chief of the committee staff, said that he and his deputy Mark McConaghy had decided to leave in the summer. Their decision had nothing to do with the outcome of the election nor with their "being mad or frustrated," he added.

There is no immediately obvious successor for Shapiro's job, which is a key one for the formulation of tax law. Their replacement will be chosen by the Joint Committee, which consists of the ranking members of the Senate Finance Committee and the House Ways and Means committee.

The chief of staff needs to be someone aware of politics and receptive to the members of the two tax committees, Shapiro said.

The election results did not make any difference to the kind of person who should get his job, Shapiro said. He has been chief of staff since early 1977 and is about to begin his 15th year as a member of the committee staff.

He pointed out that when he and McConaghy began there was a big move to reform taxes but that this had shifted to looking for tax incentives for production and investment. McConaghy has spent eight years on the committee staff and four years before that at the IRS.

This was long enough to work as a public servant, Shapiro said, adding that he would like to spend more time with his family after the long hours and high pressure of his present job.

The two tax experts want to go into private practice of some kind and to work together if possible, he went on. However they did not think it would be proper to tell anyone about their decision to leave until after the election, so now they will just wait and see if they got any offers, he said.

Both men and lawyers, but they would not necessarily work as such. "I have had plenty of lucrative offers over the years," Shapiro commented, "so it's not for money. I could have left years ago for that.