You can sometimes knock a person's ethnic background, find fault with his religious belief or question his children's manners without serious consequences. But don't ever mess with somebody's parking space unless you want all kinds of trouble.

Well, this is "all-Kinds-Of-Trouble-Week at the Parklawn Building, a leased federal facility in Rockville that always seems to have more than its share of unhappy tenants. Management at "Rockpile" (as HEW workers affectionately call it) is messing around with the parking there. And many of the employees are fighting mand.

The problem is as simple as the situation is complex. Parklawn has about 6,300 workers and 2,700 free parking spaces. Eight of 10 workers drive. You get the picture.

What management is doing is reallocating the parking spaces at Parklawn. The idea, officials say, is to give more slots to people, give early-bird workers a chance to park and eliminate "phantom" car pools. More on the latter later.

Employees says that the people in charge of parking are moving arbitrarily and in a dictatorial manner, making it tougher for working stiffs to qualify for and fit into one of those spaces, which would go for $60 a month downtown, if you could get one.

Parking cars at Parklawn say the redistribution is necessary because some people who have reserved spaces for car pools don't use them, and some people who have reserved spaces for car pools don't have car pools. An official at Parklawn said spot checks show that anywhere from 100 to 150 spaces are vacant each day in the area formerly reserved for three-person car pools. "Something," an official said yesterday, "is wrong."

One of the things that is wrong, federal officials say, is that a lot of employees have been running phantom car pools. That is defined as a vehicle, a driver, and maybe one passenger, plus two or three dummies or non-persons.

To qualify for a reserved space in the past. HEW officials said, some driver have forged the signatures of other workers to make them "car pool" members. Some people are so desperate for a reserved parking stickers, they say, that drivers have used the names of dead workers as riders, or invented people and addresses to make it look as though they are hauling more passengers than they really are. You wouldn't believe the things some people will do for a parking space, officials say.

Administrative brass say the new regulations make sense, and were approved by top managers of the five HEW agencies in the building. Some employees say it was done in the dead of the night by officials who have carefully preserved their big chunk of the 860 indoor slots.

They say HEW has changed the rules so that nonfederal workers in support jobs at Parklawn no longer count as "bodies" where car pools are concerned.

Employee groups believe that HEW management is using the phantom car pool issue hereby as an excuse. They are demanding a meeting between drivers and management to see if a more equitable situation can't be worked out. Only the 80 or so people who can and do ride bikes to work seem to be unruffled by the parking space war, which will get worse, both sides predict, before it gets better.