After 7 1/2 years of operation, Capital Centre has drawn more than 20 million spectators and kicked $13.3 million into the tax coffers of Prince George's County, according to a consultants' study prepared for Abe Pollin, chairman of the facility's board of directors.

But the study makes no attempt to evaluate the financial viability of the Centre as a sports and entertainment complex, nor does it assess long-term prospects for the Bullets basketball team or the Capitals hockey team, both of which ended their seasons this year in frustration and disappointment.

With an average attendance this year of 9,155, the Bullets experienced an 18 percent drop from 1979-80 and suffered their worst year at the gate since the Centre opened on Dec. 2, 1973. The Capitals, despite a steadily improving gate, are known to be losing money at a rate Pollin feels cannot continue indefinitely.

Moreover, the Centre, with an average yearly attendance of 2.7 million for all events, has never met advance projections that it would draw up to 3.5 million fans a year.

The study, prepared by management consultants Booz Allen & Hamilton, estimates the Centre has generated $60 million in related spending since its opening and created more than 700 jobs.

Pollin, who is known to be weighing the financial pros and cons of his continued participation at the helm of his sports empire -- he is principal owner of both the Capitals and the Bullets -- has called a press conference for this morning to discuss findings of the Booz Allen study. Usually readily accessible, he has in the last several months refused dozens of interview requests.

Sources close to the Capitals organization say the hockey team lost $3 million a year each of the two years before the beginning of the 1980-81 hockey season. Pollin, who is said to have $12 million tied up in the team, was described as looking for a buyer, although not too aggressively. One problem has been that, given the Capitals' lackluster performances -- they have never qualified for the playoffs; last season, in a 21-team league, 16 teams made it -- it has been difficult to find a buyer willing to pay enough for Pollin to recover his investment.

Pollin did not return telephone inquiries, but Earle Palmer Brown, a director of both the Capitals and Capital Centre, acknowledged the team has lost money. "I don't think that's any secret," he said, although he declined to discuss specific figures.

Ironically, despite the Capitals' financial straits, the team had its best year ever at the gate this past season. Total attendance was 471,833 for an average of 11,927 per game, up from an average of 11,037 in 1979-80. But the Caps were still only 15th in the league in total attendance, although they were one of nine teams to register an improvement over the previous year. Last week, the Capitals notified season ticket-holders that ticket prices were being raised 50 cents across the board.

By contrast the Bullets, who drew only 375,360 last year, have seen attendance fall by a stunning 28 percent since 1978-79, their peak year when they drew 524,356 in compiling the NBA's best record during the regular season and gaining the NBA finals for a second consecutive year. Bob Ferry, the Bullets' general manager, acknowledges the team has not lived up to all of management's expectations. "We may not be entirely satisfied," he said, "but we're doing all right."

Built at a cost of $16 million in a rush construction job that took only 15 1/2 months, the Capital Centre has been controversial from the outset, attacked by opponents as a sweetheart deal between Prince George's County and Pollin, a boondoggle built on publicly owned parkland for the benefit of private investors.

But supporters of the Centre have countered with the argument that the Centre pays taxes and rent for the parkland, stimulates the area's economy and spurs residential and commercial and development. Moreover, they note, the Centre was built with private capital, unlike many sports facilities around the nation.

Material compiled in the current Booz Allen study can be expected to buttress arguments by supporters of the Centre that it has been a vital contributor to the Prince George's economy.

Of the $13.3 million in direct tax payments to Prince George's, the study noted, $9.8 million came from the 10 percent tax on ticket prices, $2.9 million from real estate taxes and $600,000 from personal income taxes on county residents employed by the Centre and its key suppliers. The park and planning commission has collected $1.3 million in rental fees for the land on which the Centre is located.

Employes of the Centre, its teams and major suppliers residing in Prince George's County have drawn an estimated $26 million in pay since the Centre's opening and will receive a payroll of $3.9 million in 1981, the study noted.

Spectators at Centre events have spend about $19.4 million outside the Centre, including $10 million on food, chiefly at restaurants in Prince George's; $8 million on gasoline, and $1.4 million on hotel rooms, the report estimated.

The Centre's food concessionaire has spent $7.08 million on foodstuffs; participants and performers in Centre events have spent $4.7 million in Prince George's County for motel rooms, food and local transportation, and Centre operations have spent about $4.2 million on such items as office supplies, printing, legal and accounting services.

Approximately 392,000 free tickets to Centre events valued at $2.9 million have been distributed to a variety of public and private groups in the last 7 1/2 years, the study noted.