NEW YORK (Dow Jones)--The Institute for Supply Management's manufacturing index is expected to have slipped a bit, but remained firmly in positive territory in August.

The median estimate of 13 economists surveyed Friday by Dow Jones Newswires is for a reading of 53.0 in August for the ISM manufacturing index, down slightly from the reading of 53.8 in July. Readings above 50 point to expansion in activity.

The ISM is due to release its manufacturing index for August at 10:00 a.m. EDT (1400 GMT) on Tuesday.

After the release of the National Association of Purchasing Management-Chicago's purchasing managers index on Friday, which showed a modest increase to a reading of 53.8 from 53.4, Stephen Stanley, chief economist at RBS Greenwich Capital in Greenwich, Conn., wrote "we still look for a modest deceleration in the ISM index for August. We are forecasting a decline from 53.8 to 53.0 and are not altering that view in light of the Chicago PMI results."

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