Some Washington automobile owners found out the hard way that "special summer hours" went into effect yesterday at the D.C. Transportation Department's two car-inspection stations. As many as two dozen were turned away at the Southwest station when an attendant strung a chain in front of waiting cars at 2 p.m., according to one who was there.

Under a three-year-old policy, inspection hours are shifted in summer from the normal 7 a.m. to 3 p.m. to a schedule of 6 a.m. to 2 p.m.

However, the draft of a public announcement of the change failed to reach the mayor's communications office in time to be included in a routine weekly media release, according to deputy director Kathy Williams. So, she said, the announcement of what happened yesterday will be made today.

Lawrence Greenberg, deputy assistant transportation director in charge of inspections, said yesterday's chain-off of waiting motorists violated departmental policy. "Our policy is that if people are there at closing time, we don't close them off," he said.

The earlier summer hours are invoked, he said, because the heat and levels of air pollution tend to worsen in mid-afternoon, affecting both inspectors and car owners, and because the inspectors tend to work more efficiently in the cooler hours of the morning.