Had it not been for a sick dog and an outdated photograph D.C. police canine officer Thomas Delahanty would now be spending his days patrolling the side streets and back alleys of Washington's 3rd District. As it is, he is taking therapy three times a week and being treated like a hero while recovering from a wound left by a bullet meant for President Reagan.

The day before John W. Hinclkey Jr. stepped out from a press gallery outside the Washington Hilton and allegedly fired a volley of shots that seriously wounded Reagan, press secretary James Brady, Delahanty and Secret Service agent Timothy McCarthy, Delahanty was at home in suburban Maryland, sharing the Sunday newspaper with his wife.

Paging through the paper, the 18-year veteran of the force noticed a story about a Montgomery County police officer who had been shot when he and another man surprised early morning burglars in a New Hampshire Avenue store. The police officer's picture looked outdated to Delahanty.

"You know," Delahanty recalled mentioning casually to his wife, Jean, "I'm going down to headquarters tomorrow and get a new picture [of me] for the police file. The one I have now is [as] outdated as this one here."

The next day, the day of the shooting, Delahanty, 45, went to work at the 3rd District station. But because his dog, Kirk, was sick and at the veterianarian's for treatment, Delahanty went to headquarters to have his picture taken. He returned to the station and was assigned to the presidential security detail.

Several hours later, he was shot in the back. But the new picture hadn't been developed, and his old one was released to the press by authorities.

Six weeks have now passed, and Delahanty is at home, recovering from the delicate operation in which doctors at the Washington Hospital Center removed the bullet that had lodged an eighth of an inch from his spine. He is in constant pain, he says, but grateful to be alive.

But with pain has come rewards, recognition of a job well done. Today Delahanty will receive an award for valor from the New York City police department, the first non-New York police officer to receive it. He has received other such awards and has gotten thousands of letters from well-wishers across the country.

"One of the most difficult jobs we have in the police department is protecting the president. You never know what is going to happen. . . . As soon as that first shot went off I knew what was happening. My first thought was to protect the president, but when I regained consciousness I was in the hospital."

It didn't end there for the Delahantys. The very next day, Jean Delahanty's retina became detached. She, too, found herself at the Hospital Center, awaiting the first of four eye operations.

"The Hospital Center was fantastic," says Thomas Delahanty. "They didn't spare anything. I was in room 435 and she was right underneath me in 234, and the center even offered to put us in the same room if we wanted, but I realized it would have been very difficult for the doctors . . . We are not real religious people. We try to go to church together on Sundays when we can. But I want to tell you, we both prayed a lot during this ordeal."

And since the day of the shooting, Delahanty says, the White House has shown constant concern. Vice President Bush, Mrs. Reagan and the Reagan children have visited him, and he's received gifts, pictures and jellybeans from the president. Jean Delahanty was even invited to the First Lady's party at the Shoreham last week, where she was given a small cloth shopping bag filled with gifts.

Neighbors have pitched in to take care of the house while the Delahantys recover, cutting their lawn, cooking meals, offering a friendly ear. Thomas says he's particularly thankful to his partner of nine years, Winston H. (Smitty) Smith. Since the shooting, Smitty was detailed by his superiors, Delahanty says, to help the Delahantys through their recoveries.

"Smitty has been our cook, chauffeur, bodyguard and shopper," says Delahanty. I don't know what we would have done without him. We're closer than brothers."

With convalescence continuing, Delahanty says he's ready to go back to work. "I'll stay in canine," he says. "You win some and lose some . . . during the Hanafi takeover I almost got it then. I was chasing one of them down an alley and he opened up fire on me with an M16. It just wasn't my turn then."