For thousands of years, every boat captain has known that his most important mission is to keep his head.

Now the federal government says, "No more."

An era of confusion and turmoil comes to an end Jan. 30 when the Coast Guard begins enforcing a comprehensive new law on boat sanitation.

The head is out. The marine sanitation device (MSD) is in. And boat owner-operators who fail to comply with the new rules are subject to fines of up to $2,000.

In 1972 Congress passed the Environmental Pollution Control Act. As part of it the Environmental Protection Agency was charged with responsibility to clean up the nation's waterways.

One obvious target was boat owners, who since the beginning of time have been dumping or pumping raw sewage over the side.

According to officials of BOAT-US, a lobbying organization for recreational boaters, the EPA's initial plan was to simply issue a blanket ban on discharging anything from a boat.

Boat owners rose up in protest, saying the plan was unfeasible, and there ensued seven years of complicated backing and filling during which hardly anyone knew what to do.

There were laws for old boats and laws for new boats, laws that would have boat owners installing certain types of MSDs which would have to be replaced when new types were developed.

Most boaters just sat still and waited for something comprehensible to come along.

On Jan. 30 it happens. After that no boat operating on navigable United States waters within three miles of the coast will be permitted to use a standard, flow-through discharge head.

Boaters will have a number of options of varying expense.

The first option is simply to remove the existing head and plug up the intake and outlet valves. The Coast Guard doesn't care if a boat has no head, but if it does it must be of the approved type.

The old head could even be left in if it were permanently disconnected from the plumbing.

That option is a little less sturdy, legally, because it isn't covered in the regulations.Lt. John Busavage, chief of the Coast Guard's pollution prevention and enforcement branch, said it's a common-sense solution, approval of which would be left somewhat to the discretion of an inspecting officer.

Or a boat could be equipped with an approved MSD. There are two basic types applicable to small pleasure boats -- a flow-through chlorinator/mascerator which treats and discharges the effluent, or a holding tank that can be pumped out at shoreside stations.

There are problems with both. The chlorinator-mascerator (type I) MSD uses significant electrical current, which is subject to breakdown. These gizmos cost anywhere from $300 to $1,000 and are complicated to install.

The holding tank (type III) MSDs can cost anywhere from $50 up, plus fittings and installation. The problem with them is locating pumpout facilities. A Potomac River boatman who has a holding tank said his charts show five pumpout stations at marinas on the river, but he has yet to find one that is in operation. His solution: "I wait for high tide at night and pump it over the side. It's ridiculous."

There is also a type II MSD -- a bacterial digestion system. It involves a large and expensive installation and is not generally regarded as suitable for small boats.

Probably the most reasonable solution is to remove the existing head and replace it with a self-contained protable unit of the type popular with campers.

These portable units cost about $80 and can be carried off the boat for discharge.

Busavage said the Coast Guard figures there are about 1 1/4 million pleasure boats in the United States equipped with heads. He said his agency does not intend to "start a purge, running around to every marina checking all the boats for MSDs.

"We have no additional funds for MSD checks, so it will be part of our regular safety-check procedure." However, he said the Coast Guard does have authority to enter into agreement with state marine police to have the state agencies enforce the statute. No such agreements have been made, but he expects some states to come forward by springtime.

A boater found in violation would be subject to a warning or a citation. Busavage said warnings may be issued where the boater can show that he is in the process of obtaining or installing an MSD.

Otherwise, it's ticket time, with fines levied at the discretion of a Coast Guard hearing officer.

One thing the Coast Guard will permit is use of Y-valves to bypass the treatment or holding system when a boat is in waters three miles or more offshore. These valves must be locked, taped or wired shut in the MSD mode when the boat is in inshore waters.

The whole affair smacks of Big Brother to many boaters, a group that generally prides itself on its independence. "The amount of pollution pleasure boaters put out is negligible compared to what the municipalities and industry and farm runoff do," said Richard Scwartz, director of BOAT-US. "It appears that boat owners are a political target for an illusory accomplishment."

The aim way be illusory, but boaters are stuck with the law. As an independent breed they are already mapping out imaginative escapes.

My own personal solution goes back a few years -- a cedar bucket with a top.