Abigail, somewhere between seventh heaven and cloud nine, was at it again. I didn't mean to catch her in the act, but when I walked into the room, I couldn't have known she would be there drinking. Abigail has a problem, and here she was in the middle of a few strong sips.

It's not what she drinks--only water --but where: out of a flower vase on a desk top in a senator's office in the new $137 million Hart Senate Office Building. And it's not that Abigail isn't entitled to her water. The problem of Abigail, a 7-year-old Manx cat owned by Sen. John Melcher (D-Mont.), is one of adjustment.

It's the Hart building: a cool-sleek, glassy, uncozy structure into which Melcher and 49 other senators and entourages are now unpacking their moving crates.

Abigail was carried last week from her living quarters of six years, the homey Melcher office in the Russell building. With her was Emily, her gray-coated sister, also a tailless Manx. They are the nation's most exalted office cats. The American Cat Fancy Association gives no best- of-breed ratings for office cats. But if it did, Abigail and Emily would be at the top. They are the only cats in the world's most exclusive club, the U.S. Senate.

Abigail and Emily, as most of the club members like to say of themselves, have humble origins. Melcher, a good man and a cat lover since boyhood, found the pair in 1976 in the Missoula, Mont., animal shelter. He was moving up in the world at the time--from the House to the Senate--and thought that going from a shelter in Missoula to his Washington office would be a rise for the constituent cats too.

No Oversight Committee on Relocation Traumas has yet been appointed to learn what mental pressures the 50 senators are enduring in their new quarters. It was a move few wanted to make from the cozier offices of the Russell and Dirksen buildings. If the current edginess of Abigail and Emily tells us anything about the effects on the nerves and the psyche of being exiled to Hart, an oversight committee, and perhaps a presidential task force, should be appointed immediately.

Between Abigail--named after First Lady Adams--and Emily--as in Dickinson, the poet--Emily appears to be more mentally troubled.

A year ago when I interviewed her master in his office in the Russell building, Emily exuded friendliness and charm. When I sat, she jumped on my lap. I petted her satiny coat and she purred. Then, conferring a still higher honor on me, she sprung to my shoulder on the way to the headrest atop the armchair. There she remained during the interview, as content as the feline in Keats's "Sonnet to Mrs. Reynolds' Cat."

Last week, Emily's old self had vanished. She avoided me. Purrless and wary, she kept her silence and distance. In the new office, with unpacked boxes against one wall and an unhung mirror resting against the base of another, she was showing the tiger in her genes and the jungle in her blood.

"Don't you remember me, Emily?" I asked. She all but raised her back, as though I were the lowest of Washington's humanity--a fat cat lobbyist.

Abigail appears to be in mental turmoil, too. Scaling a secretary's desk to drink out of a vase between the Rolodex and pencil box is the least of it. Last year, she couldn't get enough of ankle-rubbing. The other day, she lurked under a desk and could bring herself only to rub the lower drawer of a cold file cabinet. She meowed several times. These were plaintive meows, as if to say, "I'm going to the dogs in this joint, take me back to Russell--or Missoula."

The happiness of their Russell years was unbounded. They could mouse and roach--pleasures not to be found in lifeless too-scrubbed Hart. For hobnobbing with the greats of the republic, they pawed down the corridor to the neighboring offices of Sen. Robert Byrd of West Virginia. All that's next door now is some fellow from Alabama who's less known than Garfield.

John Melcher understands the angst of his cats. In time, he says, they will adjust well. He is the only veterinarian in Congress and knows of these things.

I won't argue with him about Abigail and Emily. But with the cats belonging as much to the nation as to the senator, I have sought a second medical opinion on the case. Dr. Walter F. Burghardt Jr., a leading veterinary psychologist who provides therapy for cats at $45 an hour, says that many of his patients do indeed suffer mental problems caused by moves. He has professionally treated angry, anxious and emotionally shattered cats. Burghardt did not believe prolonged therapy is needed for Emily and Abigail. Some special care will probably bring them around, he said.

In the Hart building, where a rooftop tennis court will be available to ease the relocation pains of the senators, why not some perks for the cats? Start them off with a bowl of goldfish. If that doesn't cheer them, bring in a tub of salmon.