It rained on the parade of old-timers at RFK Stadium last night, but that didn't stop John Grady, who came all the way from Atlanta, from keeping up with his favorite star.

"I saw Hank Aaron hit No. 714 in Cincinnati, and then 715 in Atlanta," said Grady, 58. "If he's going to hit any more, I'm going to see it."

Grady may not know about the 40 more home runs Aaron has hit since then, but one thing was sure: he and the rest of the 29,196 fans here weren't going to let this opportunity get away, no matter the weather.

It took baseball 12 years to return to Washington. But the fans and players acted as if it had never left.

Harmon Killebrew was swatting batting practice balls into the stands while Aaron huffed and puffed and finally reached the stands on his last attempt.

Al Lopez, manager of the American League, would not give youngsters his autograph until he convinced every one of them that he was not Jim Fregosi.

Robert Merrill, wearing a Washington Senators uniform, reluctantly agreed to give his autograph, but insisted on telling the fans he was an opera singer and not a baseball legend.

The legends, of course, were most in demand.

"I just came to see Stan the Man (Musial)," said Flo Robinson of Silver Spring. "I used to take the Redbird Express up to Sportsmans Park to see him play. He's gained a little weight, but so have I."

"I came to see Mickey Mantle," said Jay Goldberg, showing his Yankee jersey. "But I don't think he's coming. I guess I'll have to root for (Whitey) Ford and (Bobby) Richardson."

And then came the rain. Undaunted, the Washington Redskins pep band, positioned in the left field bleachers, played on.

"We were told to play until we drown," said the lead tuba player.

When the dugouts were deluged, Joe Garagiola decided it was time to take cover. "I've got to get out of this rain," the nearly bald former catcher said. "It's bad for my hair."

"It will be a sloppy game with this rain," said Mickey Vernon, who then winked and added, "Of course, it might have been sloppy without the rain."

William Robbie of Washington took the bad weather more in stride. "I knew there was a reason baseball wasn't in D.C. anymore."

As the rain got harder, the possibility of a postponement increased.

The field became soaked and it seemed as if an ark would have to be built to rescue those in the flooded part of the locker room. But finally the rain let up and the old-timers game to beat all other old-timers games could begin.

"I'm having a great time," said Ron Simpkin of Arlington. "It's like being 10 years old all over again."

Simpkin then pointed to his sons, Jason, 4, and Cal, 9, and said, "They keep asking where Reggie Jackson is. They don't understand he's not an old-timer yet."

Allison Johnson, 13, of Silver Spring, was thinking along the same lines. "I wish they had newer players. These are mostly guys my dad would like--real old people."

A scoreboard with innings instead of quarters finally was illuminated and baseball was really back.

"It's just a real exciting feeling to be here," said Lou Brock, "with guys who were even my heroes."

Angelo Marie, 62, of Washington, perhaps summed the evening's mood up best.

"I used to watch the Senators play at Griffith Stadium, and then here . . . I really don't care who is playing. The place just looks a lot happier with baseball in it." Dukes-Suns Rained Out

The Carolina League game between the Alexandria Dukes and the visiting Hagerstown Suns scheduled for last night was postponed by rain. It will be made as part of an Aug. 17 doubleheader.

The Dukes open a three-game series tonight against the Southern Division-leading Peninsula Pilots at 7:30 at Four Mile Run Park.

Also contributing to this story was Doug Cress.