A blissful and bucolic land

''The idea of New England,'' writes Robert L. McGrath, an art historian at Dartmouth College, ''remains one of the most enduring inventions of the American imagination.''

He is right: The thing called ''New England'' these days is in large part an imaginative construct. For most Americans, the name does not call to mind derelict mills, sprawling suburbs, or glass-and-brick electronics plants - however much these are part of an increasingly paved and neoned New England. Instead, it evokes a post-card-perfect vision of white steeples, covered bridges , family-owned farms, and bucolic peace.

That romanticized sense of the place, in many ways, was a painter's creation. Over the years, an impressive body of American artists has been nourished on New England's values and images. To them, the region was a place of limpid light, majestic hills, wide seascapes, vegetation both lush and benign, and a relationship with nature that evidenced both man's skill and his respect.

Where did such images come from? Where, in the hands of present-day artists, are they headed? These questions are implicit in a pair of exhibitions running this summer at Dartmouth College.

One pokes into the past. Called ''The New England Image: Nineteenth-Century Landscapes From the College Collection'' (running through September), it presents 25 works by little-known (sometimes unknown) painters. The other examines the present. ''Regional Selections 1982'' (through Sept. 3) displays 50 works by six current New Hampshire and Vermont artists, selected from 16 semifinalists in last September's Regional Art Show at the Hopkins Center.

These are not blockbusters. As exhibitions, they are compact and manageable. They will not leap up and sock the viewer with their brilliance. But neither do they overload the visual circuits. Giving no more than can be reasonably absorbed in one viewing, they leave the mind free to ponder the changes in artistic perceptions of the region over the last 130 years.

The New England landscapes, drawn together by Professor McGrath, come from a neglected corner of the collection assembled between 1957 and 1965 by Churchill P. Lathrop, former director of the college's art galleries. At that time, America had yet to discover (as it would in the wake of its 1976 bicentennial introspection) the merits of its own 19th century. So these paintings - by an assortment of hands trained not only in the academic or Sunday-painting traditions but in the shops of lithographers, engravers, illustrators, furniture and carriage decorators, and sign painters - were slowly darkening with age in local antique shops. They could be had for as little as $50 apiece. Mr. Lathrop, coupling a closet fondness for that era with the college's avowed interest in the history of its region, found the funds to acquire them.

As organized by Professor McGrath and a class of 11 students last spring at the Carpenter Gallery, these works make a modest contribution to the scholarship of the period. The catalog, largely student-written, identifies unknown artists , discovers locations of some of the scenes, and traces relationships between these painters and their better-known counterparts such as Thomas Cole, Frederick Church, and Albert Bierstadt.

But the real impact of the show is less in the writing about it than in the seeing of it. For there is, in these painters, a marvelous unpretentiousness - a kind of humility before what they obviously saw as a powerful and transcendent nature. Even among the naivete of the folk artists (like the wholly obscure W. Morrison (whose ''Landscape With Ferryboat on Lake Winnipesaukee'' is shown on this page) there is a charming grace, a willingness to supply careful detail rather than painterly flourish.

With the exception of the stunning ''White Mountain Landscape,'' by the French-born Regis Gignoux, these are small paintings. In them, water is usually calm and skies bright - a hallmark of the Luminist traditions of the period. And even when the brushwork is loosened (as in the small ''Rangely Lake,'' by Benjamin Champney, the grand old man of the White Mountain School), the subjects do not escape into anything like abstraction.

If these landscapes hew to a centuries-old tradition, the works of the contemporary artists across campus in the Hood Museum of Art explore newer developments. They range from the human-size polychromed wood-and-wire constructions of Loretta S. Wonacott Barnett and the Georgia O'Keeffe-like swirls of color in the paintings of Pace Drake, to the crisp photos of John Layton and the fascinating holograms of John Perry. These are works of a newer currency, working with artistic conceptions and materials that the landscape artists could never have known.

Yet the strength of the show resides in the works of the two artists who pursue more standard routes. Elizabeth Rowland Mayor's monoprints, overlaid with pastels or oils, produce delicate but sure-handed representations of New England vegetation with titles like ''Indian Summer,'' ''Violet Grasses,'' and ''October Thicket.'' Nor is there anything shockingly inventive in the swatches of blunt impasto color that Lorna Ritz has tooled onto her large canvases. She simply has a good eye for the arrangements of masses, a skill at blending colors into one another without losing their identity, and an ability to create, in entirely abstract works, an active sense of depth and movement.

These pieces have evidently grown out of a great joy in the landscape, a feeling her predecessors across campus would have shared. It may be that none of the works at Dartmouth this summer are by artists who, in Matthew Arnold's words , ''saw life steadily and saw it whole.'' But at least they see nature fondly and honestly, as Yankees are prone to do.