There is probably no other band in rock that inspires the loyalty and affection accorded the Grateful Dead. Lovingly dubbed the "Dead Heads," these legions fill concert halls across the country, often traveling hundreds of miles to hear the group ramble through one of its standardized three-hour-plus sets.

When it comes to albums, though, the Grateful Dead have always fallen short of superstardom. Many people simply assume that the Dead are as big in record stores as in stadiums, but the fact is that they have never sold albums nearly as well as their live draws would indicate. And any three Grateful Dead records put together would not come close to equaling the sales Fleetwood Mac's "Rumours" has accumulated in just four months.

Part of the problem is the band's inherent looseness, which, though endearing live, sounds sloppy in vinyl. Also, despite some bona fide classics including "Box of Rain," "Uncle John's Band," "Sugar Magnolia," and "Friend of the Devil," the group's members are not the most prolific of songwriters and many of their efforts tend to sound the same.

Finally, the Grateful Dead lead the league in expendable "in-concert" albums. When the Dead go live, they do ti to the hilt. Not content to put down the best tracks and leave the rest on the editing room floor, Jerry Garcia and company usually release the whole shootin' match.

The result is sometimes two records, sometimes three; sometimes good to excellent music ("Europe '72", Warner Bros, 2668), sometimes dreadful ("Steal Your Face," Grateful Dead LA 620-52). There can only be so much live Dead before the Dead die.

Now the Grateful Dead have a new record company - Arista; a new producer - Keith Olsen; and a new studio album. "Terrapin Station" (Arista 7001). The tunes are tight, well-produced, melodic, and - for the most part - slick. Grateful Dead purists may well bury their Dead for "selling out," but "Terrapin Station" should infect the band with the disease afflicting all other supergroups - mass appeal. (So much so, that some fans - likening the record to recent Fleetwood Mac efforts have renamed the group either Fleetwood Dead or Grateful Mac.)

As soon as side one is one chorus into the opener, "Estimated Prophet," it is apparent that the Grateful Dead are barking up a new tree. The song is percussion-and-bass oriented and the rhythm section, especially bassist Phil Lesh, lays down a beat that is almost reggae in style. Vocals are in tune and there is no sign of lingering solo runs or free-for-all "jams" which have given the group both a large number of fans and an even larger number of detractors.

Also obvious is the prominence of Donna Godchaux's voice. Initially known only as Kieth Godchaux's wife, she is the single biggest improvement on the record. Her phrasing on her own composition, "Sunrise," is vaguely reminiscent of Annie Haslam and Renaissance. Though Godchaux doesn't have Haslam's range, the melody is perfectly suited to her own talents.

Those "Dead Heads" not already reeling from the quasi-reggae of "Estimated Prophet" will certainly shriek at the reworking of "Dancin' in the Streets." Already a hit twice (first for Martha Reeves and the Vandellas, then for the Mamas and Papas), this version has already caused some loyalists to disparage the "disco Dead." In truth, the song is not so much disco as jaunty - and the get-up-and-boogie feel does not a jukebox make. Cleverly, the Dead do their own arrangement rather than try to adapt the Motown sound to their native San Francisco roots.

Another successful cover is Bob Weir's gutsy remodeling of the traditional "Samson and Delilah," first made popular by Peter, Paul and Mary. Again, one wouldn't normally mention the Grateful Dead and Peter, Paul and Mary in the same breath, but - as with "Dancin' in the Streets" - the end justifies the means.

Producer Olsen keeps the reins on Garcia, and twin drummers Bill Kreutzmann and Mickey Hart blend superbly on the title track which takes up all of side two. Garcia seems to have sacrificed individual flash for group solidarity, and the band is better off for it.

Besides solid vocal harmonies and tasteful ensemble playing, the composition is enhanced by Olsen's subtle use of horns and strings. The band never indulges itself and Olsen overdubs rather than overkills.

This is not the average Grateful Dead extended workout so prominent on their live albums, but varied, textured music which does not lag.

The album is definitely a departure for the Grateful Dead, but one which likely marks a new direction rather than a one-time experiment. "Terrapin Station" is all the things many of the old fans may not want to hear. It also may be the stepping stone to a more generally popular - and marketable - status. And that will make a lot more people a lot more grateful.