WASHINGTON (Reuters) - The U.S. Treasury said on Wednesday it will keep coupon auction sizes steady in the July to September period, the second consecutive quarter it has maintained its coupon issuing sizes.

The department also said it would conduct a small-value test auction using its contingency auction system on Aug. 17. More details about the test will be announced on Aug. 15.

A Treasury official told reporters that the test auction, in addition to Treasury's mock auctions, was prudent planning in case of technical difficulties or a cybersecurity incident.

In line with other small-value auctions, it is expected to be in the $25 million range, the official said.

On future coupon sizes, Deputy Assistant Secretary for Federal Finance James Clark said in a statement the department "plans to address changes in any seasonal borrowing needs over the next quarter through changes in regular bill auction sizes and/or cash management bills."

In its quarterly refunding announcement on Wednesday, Treasury said it would auction $62 billion in coupon debt next week.

On Monday, Treasury said it expects to issue $201 billion through credit markets during the July-September quarter, up $47 billion from its initial estimate in May.

(Reporting by Lindsay Dunsmuir; Editing by Andrea Ricci)