I.R.S. HEAD SILENT ON NIXON PENALTY FOR BACK TAXES
IRS Comr Donald C Alexander, citing principle of confidentiality between IRS and taxpayer, refuses to say whether $432,787.13 Pres Nixon owes in back taxes includes negligence penalty of 5%, int, CBS TV program Face the Nation; does not invoke principle when he says there was no fraud penalty assessed against Nixon; Nixon's accountant Arthur Blech says he is shocked that issue of negligence has been raised as he cannot see where 'negligence lies,' int; Alexander says for 1st time that IRS's original audit of Nixon's tax returns was not as thorough as it should have been; says previous Pres were treated too leniently by IRS and that practice has been changed; exch between Alexander and CBS correspondent Daniel Schorr noted; Repr W D Mills says he thinks no negligence penalty was assessed, int, ABC TV program Issues and Answers; says it could have happened and 'we would know nothing about it'; Alexander por (L)