The Washington platoon of Arnie's Army turned out last night for a 19th-hole party to welcome the famous golfer-cum-businessman to Washington.

The 52-year-old Palmer, who still attracts a crowd of admirers when he tours the golf course, comes to Washington as a partner in Woodmere, an 800-acre residential development in Prince George's County. Rep. Robert Michel (R-Ill.), the House minority leader, and Rep. Dan Rostenkowski (D-Ill.) were the bipartisan hosts at the reception for about 150 in the courtyard of Decatur House. Guests included Secretary of Transportation Drew Lewis, from Palmer's home state of Pennsylvania.

It isn't often that two congressmen join for a party to welcome a new businessman to town. But then few businessmen are glamor-boy golfers like Palmer, who has amassed $2 million in prizes and many friends--including politicians and public officials--while playing golf.

"I first met Arnie about 12 years ago when he was my partner in a Pro-Am tourney," Rostenkowski (handicap, 18) said. "I remember Arnie teed off. As I got ready to tee off, the crowd was already moving to follow Arnie to the next hole, leaving me with only a straggle of spectators."

Michel (handicap, 14), the co-host, also said his friendship with Palmer extends back over the years to golf tourneys, including the Bob Hope Desert Classic and Pro-Am matches.

"We were friends long before I went into business," a tanned, relaxed Palmer explained as he was introduced to guests by his two congressman hosts.

The guests were asked to autograph a plan for a specially designed golf course for the nation's capital--with the first tee at the Capitol, the pro shop at the White House, and the Washington Monument as the pin marking one hole "to be removed and replaced with caution."

Among his many business enterprises, Palmer has a subsidiary that designs golf courses, including the 27-hole course for the Woodmere development, which is being planned by the Arnold Palmer-Buckley Development Co.

The championship golfer, who uses his father's old tractor to make a salesman's pitch for Pennzoil on TV commercials, also owns a Cadillac dealership and is associated with several country clubs and a sporting goods manufacturer that markets golf equipment bearing his name.

Hill and Knowlton, the public relations firm that put together the Palmer reception, called administrative officers for the House and Senate to make certain that invitations went to congressmen who were regular golfers.

"The secretary of the Senate said that he could come up with about 10. But if it were tennis, there would be about 99. That seems to be the sport on the Hill these days," a Hill and Knowlton representative explained.