Arlington Treasurer Frank O'Leary, continuing his campaign to crack down on tax delinquency, has announced the collection of more than $1 million in overdue real estate taxes, some of them unpaid since 1965.

As a result of the crackdown, O'Leary said, the real estate tax delinquencies for the last 20 years have been reduced from $2.4 million to $1.4 million. Virginia law places a 20-year statute of limitations on the collection of real estate taxes.

About $450,000 of the still unpaid taxes are due from two businesses that have been challenging their assessments in court, O'Leary said.

The $1 million collected as of June 28, the last business day in Fiscal Year 1985, covers those real estate taxes due through 1984, and meets O'Leary's goal, announced in March, of collecting $1 million by the end of the fiscal year.

Delinquency notices for those who have not paid the first installment of their 1985 real estate taxes, due last May 15, are being mailed this week, O'Leary said.

As part of the tax crackdown, O'Leary has called on the county's courts, sheriff's office and the computer systems office to track down and prosecute scofflaws.

During his 1983 campaign for treasurer, O'Leary pledged to seek out tax delinquents, complaining that his predecessor's policies had been too lax and had led to Arlington's having the highest rate of uncollected real estate and personal property taxes of the large Northern Virginia jurisdictions.