Boston — Like a police car cruising a beat, the 32-foot Coast Guard patrol boat weaves through Boston Harbor. Performing routine inspections, boatswain's mate Paul Hallman checks the mooring of ships that docked the night before, monitors pierside oil spills, and scans the general condition of the port environment.
''There's a lot of little things I guess we take for granted that the public will never notice,'' he says, pointing to a thin, 30-foot-long mustache of green moss along a rock-ribbed bank at the high-water mark. ''Five years ago pollution wouldn't have allowed anything to grow there.''
His comment underlies what some observers see as the major challenge facing the nation's fourth uniformed service. Over the years, the Coast Guard's list of duties has grown. As a result, the service's 38,500 officers and enlisted personnel (smaller than New York City's police department) may be stretched too thin by too many missions and too few dollars.
Mention the United States Coast Guard, and people most often think of helicopters hoisting hapless sailors out of storm-tossed seas. Search-and-rescue operations, in fact, remain its first priority. But it's duties also include boating safety, port security, regulatory control over the marine transportation industry, and polar icebreaking. In recent years, these duties have expanded to include policing the new 200-mile fishing and economic zones, stopping drug traffickers, halting the flow of illegal aliens, and enforcing US water-pollution laws.
''The Coast Guard always does its best with what it has,'' writes L. Edward Prina, a national expert on maritime issues in Seapower magazine. ''Unfortunately, it hasn't been given the wherewithal in recent years to realize its full potential.''
''If it weren't for the fact the Coast Guard always has people good at a lot of different things, it would cost the nation a lot more to keep the force in place that we do have,'' says William Woodward, staff director for the US House Coast Guard subcommittee.
The total Coast Guard budget equals little more than 1 percent of the US defense budget, Mr. Woodward says. In fiscal 1981 and '82, its budgets were level-funded and the 1983 allotment was raised by only 3 percent. Woodward adds that it was a victory of sorts that the Coast Guard budgets during these years weren't cut.
He cites the recent crackdown on drug traffickers as the lastest example of the Coast Guard being asked to take on more duties without more resources.
''The drug interdiction buildup called for by the Justice Department came without any additional funding,'' he says. ''You can't expect them to do this without cutting other areas, and some of the other areas are at least as important as drug interdiction.''
For example, he says, ''Training is an absolutely critical area and it is not being addressed to the extent it should.''
Rear Adm. Richard A. Bauman, in command of the First Coast Guard District in New England, disagrees with the assertion that his personnel are stretched too thin.
''When we go after a suspected drug runner, we have a lot of back up. More than just the ship on the scene,'' he says. ''The druggies know when we're out there, we can handle anything they have.''
But the issue to some observers is not whether the service can handle individual drug seizures, but how much money or manpower is left for other responsibilities while units are off chasing drug runners.
In time of war, control of the Coast Guard shifts from the Department of Transportation to the US Navy. Many military planners are anxious about just how credible a ''force in waiting'' the Coast Guard is, given the aging condition of its fleet. The hulls for many Coast Guard ships are at or beyond their expected useful life. The keels of the Hamilton-class cutters, seagoing workhorses, were laid in 1936.
Fleet conditions have prompted one House Coast Guard subcommittee member to say that he expects to see a Coast Guard crew on the evening news being pulled out of the water by Haitian refugees.
''That's nonsense,'' Admiral Bauman says. ''We are always under the vision of other boat owners and operators. Our people are just not going to allow their units to be anything but ready.'' He points out that the Coast Guard has scheduled the construction of 15 new medium-endurance cutters, which will replace the current fleet.
''Nine are already under construction,'' he says. ''And we have some of the highest technology ships in the world. . . .
Tight budgets also prevent the Coast Guard from getting more involved in helping third-world countries - a role Woodward and others advocate.
''The US Coast Guard is the 10th-largest navy in the world right now,'' he says. ''It can offer training in what is realistic for these countries' navies - domestic law enforcement, fisheries patrol, search-and-rescue operations, pollution monitoring.''
''When Guyana became independent of Britain, we went down there,'' says Admiral Bauman. ''A big grey warship might have caused problems, but our white hull is recognized around the world as a life-saving force, so they welcomed us with open arms.''