They're off and running at the Senate Commerce Committee. After faltering at the finish line when Congress adjourned last year, the interstate horseracing act - a bill designed "to protect and further the horseracing industry in the United States" - is back again.

It got a royal reception yesterday before the Commerce panel, where critics had waggishly threatened to start humming "My Old Kentucky home". Presiding was Sen, Wendell Food (D-Ky.). The leadoff witnesses were Sen. Walter D.Huddleston (D-K.) and Thruston B.Morton, the former Republican senator from Kentucky who is now president of the American Horse Council (representing "the entire equine industry") and chairman of the board of Churchill Downs.

The bill would completely ban interstate off-track parimutuel betting, such as that conducted by the off-track betting (OTB) corporations of New York and Connecticut. All three Kentuckians foresaw disaster to the racing industry if the measure doesn't pass.

"Off-track betting on an interstate basis constitutes one of the greatest threats to racing today," Morton intoned, envisioning a doomsday prospect of a nation hooked on OTB. "Briefly put," he warned, "if interstate wagering on horse foresees a closing of almost all racetracks around the country and the survival of only three or four racing centers in the United States. There would be no need for the 200 racetracks which we have today."

Kentuckians have been especially annoyed at New York's OTB corporations since 1971, when they began insisting on offering bets on the Derby without the consent of Churchill Downs. Wendell Ford picked up the theme:

"New York can do anything it wants to. Just don't lean on Kentucky. We've got fast horses, beautiful women, bourbon and cigarettes and they're all habit-forming."

Critics say the "bookies and breeders relief act," as a recent New york Times editorial labeled it, could effectively doom off-track betting in the two states that have it - New York and Connecticut - and prevent its inception in states that are thinking about it, such as Massachusetts and Illinois.

"It's a great finesse," declares James E. Ritchie, former executive director of the National Gambling Commision, who signed up this month as lobbyist for the outnumbered National Association of Off-Track Betting. "Very few states can have year-round racing. OTB's need interstate betting. They're government agencies. They can't just lay people off every so often. If you ban interstate offtrack betting, you doom a government entity."

The horseracing industry and its friends, however, seem bent on prohibition. Complaints that the bill would put Congress in the position of telling the states, for the first time, what kind of gambling they can conduct have made little impression so far.

"We've been a big brother to everybody else up here," Ford exclaimed."Why not here?"

George Smathers, the ex-senator from Florida who is now general counsel for the 2 million-member horse council hovered about approvingly, first at the witness table, then in a front-row seat, anticipating passage through the Senate this year.

Drafted with the help of John J. Mullenholz, one of Smather's law partners, the bill was first introduced last year by Rep. Fred B.Rooney (D-Pa.) and gathered enough support to reach the floor over the opposition of the House Rules Committee. It won House passage last Sept. 21 by a top-heavy vote of 315 to 86, and the expectation is that it would pass there again without much difficulty.

"It's just to test the waters over here," Smathers said during a recess of this year's decision to try the Senate first. The bill was blocked in the final hours of the last Congress by objections from a few senators such as Adlai E.Stevenson (D-III), Howard W.Cannon (D-Nev.) and Edward M.Kennedy (D-Mass.)

Urged on by officials of the Longacre track and other racing interests in Washington (D-Wash.), the powerful chairman of Senate (Appropriations), agreed to be the prime sponsor, heading an impressive list of racing-state senators - McIntyre (Rockingham Park), Mathias (Pimlico), Biden (Delaware Park), Stone and Chiles (Hialeah, Calder and Gulfstream), among others. "Maggie" hadn't even planned to hold a hearing until Cannon and Stevenson sent letters of protest. Even then, Magnuson urgen witnesses yesterday to be brief since the issues had, in his view, been "quits thoroughly digested by witnesses on the House side" last year.

Cannon, who stands up for legalized gambling when the opportunity arises, protested all the gloom-end-down warnings, such as Huddieston's prodiction of a "9 1/2 per cent reduction in the number of horses and people" now employed at racetracks" if interstate offtrack betting is allowed to reach its logical extreme."

He also took issue with the notion that interstate OTB, would somehow promote illegal gambling. To the contray, Cannon said, the propossed bill would hearten the bookies by taking away their legal competition. As it stands, the interstate horseracing act wouldn't touch the bookies because they don't offer "parimutual pool wagers.

Some critics of the measure also got their say, but others such as New York City OTB president Paul Screvane and his contingent were told to come back next month after waiting around with testimony stating that - except for the derby which New Yorkers contend is in "the public domain" - they have never offered a single out-of-state race without the consent of the host track and its state racing authorities.

At another point in the hearing. Morton conjured up for the committee's horror a vision of a plush theater in downtown Chicago offering four big-name televised races from distant states, along with "a gourmet meal and bottle of wine," that would absolutely devastate the nags at Arlington Park.

But the president of Arlington Park, Joseph F. Joyce Jr., testified that Illionis authorities were perfectly capable of preventing such competition. Declaring that "propely structured" offtrack betting might prove a blessing rather than a curse, the racetrack executive urged the committee to "save the racing industry from itself" and reject the bill.