The Washington Bullets yesterday landed the experienced ball-handling guard they have sought virtually all season when they acquired Tom Henderson from the Atlanta Hawks for Leonard Robinson. The deal also gives the Bullets the Hawk's No. 1 draft choice in 1977 or 1978.

The 6-foot-3, 190-pound Henderson will join the Bullets in New York today and said he expects to play in tonight's game against the Nets.

The Bullets have been beset with problems at the playmaking guard spot all season. Coach Dick Motta finally benched Dave Bing in favor of Larry Wright three games ago.

Ironically, the Bullets are currently playing their best basketball of the season, having won nine of their last 11 games. They are three games above .500.

Normally, a team doesn't make a major change when it is going well. Motta disagrees.

"The best time to make a trade is out of convenience and not out of desperation," he said. "We weren't desperate, and we got what we wanted."

Although playing for the lowly Hawks, Henderson, who will be 25 Wednesday, is second in the National Basketball Association in assists, averaging 8.4 a game. He leads the Hawks in minutes played and in steals. He is averaging 11.3 points a game and was Atlanta's floor leader as well.

He was the seventh player chosen overall in the 1974 draft. He was a starter on the 1972 United States Olympic team and played at San Jacinto (Texas) Junior College and the University of Hawaii.

Motta said the Bullet general manager Bob Ferry "researched Henderson pretty damn close and he is definitely the type of player we want."

Motta added that Henderson wouldn't be handed a starting spot, however. "It's still Wright's spot," Motta said. "Henderson has to beat him out."

"Tom has the talent to complement all of our guards," Motta said. "By his stats, it's obvious that he prides himself in assists and that's what we need.

"As I project him in my mind, he is a good defensive player. He's big, quick and a floor leader. He's both mentally and physically tough and can get the ball to the shooters. There's still the mystery if he will fit in or not, though I don't think there will be a problem."

Henderson said he kew "something was going on and the trade did not come as a complete surprise to him.

"I think i can help Washington," he said. "At least, I hope I can. I think I'll fit in okay."

Asked how difficult it has been for him to keep setting up his teammates for shots while the Hawks have lost 30 of 46 games, Henderson laughed and said, "I think to assists just like a scorer would points."

Assuming Henderson beats out Wright, the latter would probably become the third guard, with veterans Bing and Bob Weiss adding stability.

Robinson wanted to be traded.

He started every game for the Bullets this season, but his playing time had diminished the last few games. He is still averaging 16 points and nine rebounds a game.

The 6-7, 225-pound, 25-year-old Robinson, who was drafted by the Bullets in the second round in 1974, plays a style very similar to that of Elvin Hayes and he feels he was somewhat miscast as a small forward.

The trade wasn't a surprise to him either. He is the bait the Bullets have dangled all season.

"It's all right with me," Robinson said after learning of the trade. "Whatever they (the Bullets) think they can do to improve the team they have to do. I was expendable here, but I know I'm going to play 10 more years somewhere.

"The Bullets got what they wanted, a big, strong, playmaking guard. They had to make the deal. Atlanta gave up a lot to get me, so they must really want me, too. That's good."

Robinson will get his wish and play the big forward spot with the Hawks with John Drew as the small forward. Robinson relishes the thought.

"It'll be interesting," he said. "Playing big forward will keep me closer to the basket. That should help me.I'll get more blocked shots, more rebounds and I'll get more of the type of shots I like. I'll be right at home."

Motta was noncommital about who would replace Robinson in the starting lineup. It will be either Leonard Gray or Kevin Grevey. Gray has been playing ahead of Grevey lately, but Motta is very high on Grevey.

Motta added that this is the first time he has ever traded a starter during the season.

"Leonard was a good player," he said, "and he was very much in demand. This was a major decision and nothing to be taken lightly."

Robinson is in the last year of the original three-year contract he signed as a rookie. Henderson has two more full seasons to run on his contract.

Here is how the plan for determining what draft choice the Bullets will receive works:

The last-place team in each conference flips a coin at the end of the season to decide who gets the first pick in the draft. Under the terms of the trade agreement, if the Hawks are involved in that coin flip, the Bullets, who already have two No. 1 picks in the 1977 draft, will get the Hawk's No. 1 pick in 1978.

If Atlanta is not involved in the coin flip, then the Bullets have the option to exchange No. 1 picks with the Hawks in 1977. So, conceivably, the Bullets could obtain the third pick in the entire draft this year.

If they do not exercise that option, the Bullets will automatically get Atlanta's No. 1 pick in 1978 and the Hawks will get the Bullets' second pick that year.