Martin Feinstein, who has been general director of the Washington Opera, will become president and chief operating officer of the National Symphony effective immediately, former NSO president Austin Kiplinger announced yesterday.

The position of managing director held for the past three years by Oleg Lobanov, has been abolished, and the orchestra's bylaws are being changed to make Kiplinger the chairman of the 75-member board rather than president.

Feinstein said yesterday that he is taking the new position "at a time of great problems and great opportunities. Although I am thrilled, I would also be a fool if I weren't also terrified. There is so much that has to be done."

Upon accepting the NSO job, Feinstein resigned from his position as the Kennedy Center's director of opera and ballet, but will keep his position with the Washington Opera. His NSO salary has not yet been settled, but reportedly will be slightly more than the $50,000 he will receive annually from the opera company. "The orchestra will not be hit too hard," he said, "because I am already drawing another salary."

No plans have yet been made to fill Feinstein's former position with the Kennedy Center. He had various projects -- such as festivals and visiting opera and ballet companies -- planned into the 1981-82 season. These now become the responsiblity of Kennedy Center board chairman Roger Stevens. "I am sure they will be carried through," Feinsteiin said.

Stevens, in a statement issued yesterday, said the appointment of Feinstein was "a move in the right direction for the orchestra."

Feinstein has been a center of controversy -- and the moving spirit behind many spectacular events -- at the Kennedy Center since he took the position of executive director of performing arts there in 1972. His tenure spanned the Bicentennial, which lured such internationally famous opera companies as La Scala, the Bolshoi, the Berlin Opera and the Vienna State Opera to perform in the Opera House. He has also been responsible for a variety of festivals, and last summer, as an experiment, ran a summer opera season. According to some Kennedy Center insiders, the budget deficits incurred by some of these events were a factor in the decision late last year to terminate his services in that position.

The most pressing and immediate problem Feinstein will face in his new position will be the orchestra's deficit, presently estimated $1 million in a total budget for the current season of $7.1 million. The orchestra is trying to cut that deficit approximately in half by finding a government subsidy for the $500,000 annual rent it pays the Kennedy Center.

Kiplinger said yesterday that the orchestra is conducting a major national campaign to find corporate sponsorship. Discussions are in progress with several government agencies, including the Office of Management and Budget and the Department of the Interior (which operates the Kennedy Center), about the possibility of having the NSO declared the center's orchestra-in-residence and its rent subsidized.

While it is in financial stratis, the orchestra --now approaching its 50th anniversary -- has recently reached unprecedented heights of prestige and critical acclaim. The unification of its leadership with that of the Washington Opera under Feinstein (although he is working under two separate contracts) may be a logical step toward integrating the two organizations. One obvious model might be Vienna, where the State Opera has the prestigious Vienna Philharmonic serving as its opera orchestra.

Feinstein admitted yesterday that he has long had "dreams and aspirations" about such a situation, but said that it is much too soon to say anything concrete. The contracts with members of the NSO and with members of the opera company both expire at about the same time late in 1981, and that might be a logical time to begin changing the structures.

Meanwhile, Feinstein said, "we expect the close relationship between the opera and the orchestra to be healthy for both organizations and for the community. How things will work out is still uncertain, but where they can, each will help the other."

Kiplinger said that in deciding to appoint Feinstein, the NSO board was "adding another dimension to the orchestra -- a world-renowned expert in touch with all the artistic greats." This may mean that Feinstein, who became a close friend of most internationally famous musicians during his 20 years with the Hurok organization, will be expected to lure more big-name soloists and guest conductors to the orchestra to help ticket sales. Some significant steps in this direction have already been made by music director Mstislav Rostropovich, an internationally famous cellist, who has been know to swap guest appearances with famous conductors.

On his relationship with Rostropovich, Feinstein said, "We have had a very close, warm friendship since Slava's debut, and we're both very happy and excited about working together. It doesn't sound quite right to talk about a 'harmonious' relationship when the subject is music -- so I'll say that the harmony between us will be more like Mozart than Dallapiccola."

On the division of responsibility, he said he had promised Rostropovich that "I won't conduct anything but the 'Hallelujah Chorus,'" as he does each year during the orchestra's "Messiah" sing-along program.

Oleg Lobanov, who was informed of the board's decision to terminate his contract last Friday, was reluctant to comment except to say, "I think the decision was wrong, and it hurt me very deeply."

He said that he had discussed the reasons for the decision with Austin Kiplinger but preferred not to comment on them.

"The only other thing I would like to say," he added, "is that this is an orchestra that I love very much. Because of that and because I respect Martin Feinstein, I wish him well."