If you are a 19-year-old who hasn't registered for the draft as required by law, don't say the government didn't give any warning, that it plans to come after you.

Of course, it's a vague warning -- the notice in the Feb. 17, Federal Register (page 12580) -- that the Selective Service System is establishing a new set of records to be entitled "Suspected Violator Inventory Monitoring System (SVIMS)."

Under the Privacy Act, Selective Service, like all other government agencies, has to give advance notice to Congress, the Office of Management and Budget, and to the public through a notice in the register of any new records system it plans to use involving information about individuals.

The materials to go into the new SVIMS aren't exactly investigative, per se, according to Selective Service officials. They are the substance of unsolicited letters that are trickling into the service's Washington headquarters, mainly from mothers of sons who have registered.

They disclose the names of one or more neighbors' sons who didn't, according to one official. "If their child has to register," this official said recently, "these mothers want others to do the same."

There are also bravado letters from individuals who say, "I'm not going to register," and seem to dare the government to do something about it.

Up to now, Selective Service hasn't -- except to keep all these letters in a general correspondence file.

But now that is about to change.

In mid-March, if no objection is received from OMP or the Congress, Selective Service will begin transferring the names from the letters to its new, SVIMS "suspected violator" files, and there they will be compared to the data base of 19-year-olds who have registered.

If the names in the letters don't turn up, service officials say, they will pass them on to the Justice Department for further investigation.

Of course, the Reagan administration could change all this. The president campaigned against the draft registration act, and should have it repealed, SVIMS might never get started.