Arnold Palmer, as big an attraction as ever, even when he plays on expanding senior tour

Arnold Palmer may be one of golf's ''senior citizens'' now, but you'd never have known it at the Marlboro Country Club last weekend. The familiar aura of excitement was there every day, and so was the latest version of ''Arnie's Army, '' with huge, adoring galleries following his every move. Finally, to complete the picture, he dominated his field the way he once overwhelmed the entire golf world -- shooting 68-70-69-69 to win the $150,000 Marlboro Classic by four strokes with an eight-under-par total of 276.

Of course it wasn't a regular tour event, but part of the relatively new and increasingly popular Senior PGA Tour for golfers 50 and older. This hardly mattered, however, to the spectators, who were getting a chance to see Palmer, Sam Snead, and such other old favorites as Billy Casper, Art Wall, and Bob Goalby in action. And it certainly didn't matter to the players, many of whom still compete at times on the regular tour, but all of whom realize that events like this provide a much better shot at such enjoyable pursuits as winning tournaments and cashing checks.

There have been a few senior events for years, of course, but the senior tour as a formal entity was introduced only in 1980 with four tournaments. It grew to seven in 1981, with 12 scheduled this year and a strong possibility of continued growth in years to come.

''This tour certainly has a future,'' said Palmer. ''The possibility of it being a very important part of golf is very great. A lot of areas are starved for golf. If we wanted to, we could have a tournament every week. Making sure we have the right kind of tournaments, with purses where we want them, precludes that. But I see a growing interest -- especially as more of those young 50 -year-olds come in and the competition gets even better.''

Palmer, now 52, is the key, though, for while some other seniors are reasonably popular, he is the only one whose name alone guarantees the success of an event. He has done well in such competition, winning the 1980 PGA Senior Championship and the 1981 USGA Senior Open and posting several other high finishes. He says he enjoys it, too, and will play in them whenever he can. But Arnie, as always, is juggling an eye-popping schedule which includes a couple of imminent trips to Europe and two weeks of shooting TV commercials, not to mention his newest venture supervising construction of a golf course in China. Also, he intends to continue playing with some regularity on the regular tour.

Amazing as it seems, considering the near-mythic proportions of his popularity even now, it's been two decades since Palmer's heyday of the early 1960s when he won all seven of his major championships (the 1960 US Open, the ' 61 and '62 British Opens, and the '58, '60, '62, and '64 Masters). It's pushing 10 years, in fact, since his last regular tour victory of any sort (the 1973 Bob Hope Desert Classic). Yet Arnie refuses to give up hope that he might have one more triumph in him.

''I'd like to win another one before I'm through,'' he said. ''I still feel I can do it.''

A perfect time, of course, would be this week in the US Open at Pebble Beach, but he knows full well that both the traditionally toughened-up Open course and the competition (Jack Nicklaus, Tom Watson, Ray Floyd, etc.) will be a lot more difficult.

''I know I'm going to have to hit the ball a little bit better out there,'' he conceded.

Palmer's upcoming schedule is a wild one even by his own nonstop standards. After Pebble Beach he'll spend a couple of weeks doing TV commercials, then go to Portland, Oregon, to defend his USGA Senior Open title. Next come two weeks in England wrapped around the British Open, then in August it's the PGA Championship in Tulsa and a senior event in Denver. After that come trips to Paris and Spain, followed by the World Seniors Invitational at Charlotte, N.C. And sometime he also has to go to China for his part in the golf course deal there.

''It's at a big resort hotel in Canton and the whole thing is being sponsored by Hong Kong businessmen -- working with the government, of course,'' he said. ''We'll wait until it's already under construction, then I'm supposed to go over to lend my whatever to it.''

Palmer said as far as he knows there are no golf courses in China at the moment, though supposedly there was once a nine-holer in Peking. He said he couldn't give a target date for completion because of the uncertainty about when construction will actually get under way. He also indicated that it was projected as a recreational course, with no likelihood that it would host any big tournament -- at least in the foreseeable future.

Even with all his activities, Palmer finds time to take a stand when he sees something he considers amiss -- as he did recently in a letter to Tour Commissioner Deane Beman.

''. . . I have become more and more aware of discourteous and ungentlemanly behavior and thoughtlessness of certain of our leading players that are despicable to me,'' he wrote. ''It could have long-range and negative repercussions. . .''

Palmer cited instances of players being abusive toward volunteer workers and spectators, and also toward amateurs during pro-am tournaments. He suggested that since wrist-slapping fines weren't much of a deterrent in today's financial atmosphere, suspensions might be more appropriate.

''I just said some things I thought should be said, and they got a lot of publicity,'' he said when asked about the letter. ''The response I've received has been positive. Most of the players agree with what I said.''

Could golf be heading toward the sort of behavior problems now faced by tennis?

''No, nothing that bad,'' he said. ''There was just some conduct unbecoming to professional golfers, and I suggested that something be done in such cases. I think my proposals will have an effect -- very definitely so.''