THOSE WHO LAMENT the decline of the Senate will soon have further cause. Robert Stafford of Vermont is retiring. The Senate will be both a louder and a lesser place for his departure.

Sen. Stafford, now 74, has spent his entire adult life in public service and not lost sight of what that term means. His career has been the old-fashioned, orderly kind, proof of the virtues of unhurried apprenticeship. He was prosecutor, state attorney general, lieutenant governor, governor, then spent 10 years in the House before his 15 in the Senate.

Too often the modern senator seems to be a telegenic wonder with an attention span measured in nanoseconds -- all hare, no tortoise. Sen. Stafford is by contrast substantive, unassuming, patient and effective. He is not an ink hound. He has actually been known to pass a bill before its deadline.

His areas of greatest interest have been the environment and education. In the six years from 1981 to 1986 when the Republicans controlled the Senate, he was chairman of both the environment committee and the education subcommittee. He remains the ranking Republican on each.

Environment and education were two of the areas in which the early Reagan administration exhibited its greatest revolutionary zeal. You remember James Watt. You may also remember the president's proposals, some of which sadly continue to be made, to slash federal aid to higher education more or less in two.

Sen. Stafford quietly helped to stave off the craziness. Administration efforts to hollow out the major environmental statutes in the name of deregulation were turned aside. For a while, environmental policy was a nasty draw. More recently, some of the protective statutes have actually been refreshed and strengthened. The senator from the Green Mountain State played an important part in this turnaround. He did the same in education. Last year, his last as chairman, Congress reauthorized and secured the basic forms of aid to higher education. This year it is doing so at the elementary and secondary levels. The elementary and secondary bill passed the other day, 97 to 1. The vote is a tribute to a climate that Sen. Stafford helped produce. The Senate named the bill after him.

Sen. Stafford helped to save something else in the Reagan years. By virtue of the efforts he and others made, there continues to be room in his party for its moderates. When quiet men like Robert Stafford go, they are missed.