The National Audubon Society has decided to move its national headquarters to Washington from New York City to reduce its leasing costs and to be closer to the federal government.

The new headquarters probably will be on Capitol Hill, and 120 staff positions will be moved, said Charles Scott, senior vice president for administration and planning for the society.

The society will move as soon as it signs a lease here and negotiates an end to its New York lease, Scott said.

The decision to move from midtown Manhattan came after the society realized that its rent probably would double if it renewed its current lease, which expires in 1986, Scott said.

While 80 percent of the group's work could be done anywhere, the other 20 percent involves the government, making Washington the logical place to go, he said.

"From a financial point of view, I think it will pay," he said, though he added that this kind of move is expensive initially.

Scott estimated that more than 85 percent of the country's major conservation groups have headquarters or a major office here.

Brock Evans, vice president for national issues at the society's D.C. office, said the move was spurred by New York's escalating rents but probably was inevitable.

"This is the new Audubon, you might say. We want to be very much a part of the decision-making process and on the scene," Evans said.

The society is thinking of eventually building its own headquarters, and already has been approached by officials of various suburban jurisdictions making a pitch for relocating there, Scott said. He said there has been no contact with District officials.

A number of associations and other groups have been relocating to Washington as they focus more of their attention on the federal government. The numbers have slowed since a rush of such moves between 1979 and 1981, said Frank Martineau, editor and publisher of Association Trends, a trade newsletter. But about one-third of the major association headquarters are here now, and those based elsewhere have increased their Washington presence over the past five years, Martineau said.

The National Association for the Advancement of Colored People (NAACP) was among the most recent to announce it would move here from New York City because of the high rents there and is negotiating with the city's Redevelopment Land Agency to buy the former Hines Funeral Home at 2901 14th St. NW.