To watch the chairman of the House Ways and Means Committee pursuing votes down a supermarket aisle, patting babies and lunching on a tamale at a senior citizens center is to appreciate the scare that voters are giving their congressional leaders this year.

On the road just as dawn breaks over the freshly snow-capped eastern Oregon mountains and still going strong long after dark, Democrat Al Ullman is campaigning as rarely if ever before in his 24-year House career. No crowd is too small -- even four students and three teachers at a high school the other day -- to merit nearly an hour of his attention.

Moreover, taking an unabashedly parochial view of his exercise of power, Ullman describes his lofty perch in the House as an "Oregon chairmanship . . . a rural chairmanship" from which he can protect the Northwest and rural communities from the urban East and California.

"If he'd done that sort of thing earlier on, he wouldn't be in the trouble he's gotten into now," observed Jim Ogle, a Democratic state legislative candidate from Ullman's 2nd Congressional District.

"He's had the advantages of high office in Washington and now he's seeing the other side of the coin," said another Democrat, a long-time supporter, who thinks Ullman has taken his district for granted too long and is now paying the price.

Like many other Republican challengers this year, Denny Smith, 42, a conservative political novice and weekly newspaper publisher for Salem, is seeking to portray his opponent as out of touch, too liberal, absentee -- a congressman more fond of power in Washington than of his constituents back home.

After a shaky start that almost enabled a virtually unknown liberal challenger to trip him up in the May Democratic primary, the 66-year-old Ullman has campaigned relentlessly to hold onto the narrow lead he had last summer, taking nothing for granted out of fear he'll lose the slow-to-decide voters as he did in the primary.

Smith, using the same media consultants that have packaged hard-hitting anti-incumbent campaigns against other endangered Democrats like Rep. Morris K. Udall of Arizona, is playing straight to Ullman's weaknesses.

Smith's favorite television ads juxtapose his Oregon home with Ullman's suburban Virginia residence and Oregon post office boxes and says, "It would be nice to have a congressman who likes to live here."

Smith has also profited from Ullman's advocacy last year of a value-added tax, or national sales levy on the increased value of commodities at each stage of production, in order, Ullman said, to roll back income and Social Security Tax. Oregon has repeatedly rejected a sales tax, and the idea bombed in both Ullman's committee and his district.

Ullman has long since scuttled the tax idea, lamenting recently to supporters here that, "You get your head a little above the ground and you get the hell clobbered out of you." Supporters say most but not all of that damage has been repaired. However, the episode reinforced suspicions that Ullman had lost touch with Oregon and gave Smith a running headstart on the tax issue, which should have been Ullman's strong suit as chiarman of the House tax-writing committee. And recently Smith hosted a well-attended appearance by Rep. Jack Kemp (R-N.Y.) to extol Republican tax-cutting alternatives.

Although the Oregonian newspaper reported recently that few Oregon members of Congress own property or spend much time among their constituents, Ullman has paid heed to the absenteeism issue by buying a condominium in Bend, Ore., and turning up nearly everywhere in his 72,000-square-mile district, which stretches from range and timber lands along the Idaho border across the Cascade Mountains to the capital at Salem in the relatively populous Willamette Valley.

If the value-asdded tax is Ullman's albatross, Smith created one of his own in suggesting that voters be given a choice between a financially strenthened Social Security system and private retirement insurance. Ullman jumped all over this one, claiming a "voluntary" Social Security system would soon wither and die. Like Ullman on the sales tax, Smith has been forced to backpedal. Smith's full-blooded conservatism also led him to suggest that the federal government should get out of the water and sewer grant business, enabling Ullman to raise the cry among Oregon townfolk that Smith would take away their grants.

And if incumbency has its drawbacks this year, Ullman demonstrates it still has advantaages. Smith's forces can do little more than grumble, for instance, at the recent announcement of $26 million for a new bridge in the Salem area -- a geographically small but populous section west of the Cascades where Ullman must build a big enough margin to offset Smith's inroads in more conservative and economically depressed eastern Oregon.

Although a novice at campaigning, Smith is an attractive, clean-cut sharp-spoken candidate, a former Air Force and airline pilot and the son of former governor Elmo Smith. Ironically, Ullman's relatively bland, sometimes verbally awkward style helps dispel any damaging notion of a slick, Eastern Establishment broker, although he has recently gotten rid of three-piece suits that look out of place among the wool shirts of eastern Oregon.

A third candidate, Lloyd Marbet, is running as an anti-nuclear-power activist and could hurt Ullman if the race is very close, although Marbet is expected to get few votes and may get most of them from people who wouldn't vote for Ullman anyway.

Neither Ullman nor Smith is hurting for money, and campaign spending could well exceed $1.5 million, a runaway record for the district. Smith claims to have raised more in 10 days than all of Ullman's previous GOP challengers combined, and Ullman, reaping the mixed blessings of being the leading congressional tax-writer, counts David Rockefeller, Henry Ford and the chairman of several blue-chip coporations among his campaign contributors.