By the mid-1980s, there will be but seven major convention cities in the United States, says Eugene L. Beckerle, director of the convention center in St. Louis.

These cities, not necessarily ranked by size of visitors, will include Las Vegas, Atlanta, Chicago, Dallas, Anaheim and St. Louis.

The seventh city either will be San Francisco or Washington, D.C., according to Beckerle's assessment of the potential market. San Francisco planners are contemplating a $75 million center that would be 30 percent larger that the new complex here.

District of Columbia government and business leaders want to construct a $110 million convention center in the capital city's downtown area, with exhibition space somewhat larger than in the St. Louis center.

But, the Senate opposes spending for the center, holding up consideration of the city's entire budget for the current fiscal year.

In Beckerle's view, San Francisco may get the jump on Washington and deal a death blow to potential success for a D.C. center - because the biggest conventions are planned so far in advance.In St. Louis, for examples, convetion booking dates include many weeks well into the late 1980s.

"It's hard for me to believe what's happening in Washington," said Beckerle during an interview and walking tour of the St. Louis center - the newest on the North American continent and by all accounts an instant success.

The $35.6 million Alfonso J. Cervantes Convention and Exhibition Center, owned by the City of St. Louis, has exhibition space alone covering 240,000 square feet. It is located at the northern end of the city's downtown business core.

Completed one month ahead of schedule last March 31 - partly because of an unusual pact with St. Louis labor unions - the new St. Louis convention center entertained its one millionth visitor last week.

Beckerle said business at the new complex has been growing at a rate far ahead of the most optimistic projections.

During the mid-winter period from Jan. 1 through March 31, for example, more than 600,000 visitors are expected in the complex's exhibition or meeting halls. The American Bowling Congress has moved in through May 16, for which the center has constructed 40 bowling lanes to accommodate 33,000 bowlers, with seating for 2,500 spectators at a time.

For the fiscal year ending April 30, the St. Louis center has booked 138 days of meetings or shows not projected a year ago, according to Beckerle.

"It's been a great thrill," he said, pointing to data showing the true economic impact of a center such as his, named for a former St. Louis mayor.

Because previous meeting facilities here could not handle the largest conventions - those with massive exhibition space needs - Beckerle calculated that about 130,000 of the convention visitors in the first year of the new center would not otherwise have come to St. Louis.

Because the average convention-goer stays here four days and spends $62 a day, that's a $32 million addition to the greater St. Louis economy. In the convention center's second year, Beckerle expects to double that impact.

According to the Federal Reserve Bank of St. Louis, such money pumped into the economy from outsiders trickles throughout the area, changing hands five times in 20 days - providing jobs and business for hotels, restaurants, entertainment firms, convention workers, truckers and retail stores.

But the new convention center here is adding more than dollars and jobs to the local economy. It is a symbol of what St. Louis business leaders call a new "spirit" that is evident in rehabilitation of the metropolitan area's central business district.

And it is being financed in large measure by the visitors themselves, through hotel tax revenues that provide annual payments on bonds that financed the center.

Even more important, perhaps, the center would not be a reality today if local business enterprises had not contributed their stockholders' profits as an investment when it became clear that the center would cost more than provided by the initial $25 million bond issue.

St. Louis city voters approved that bonding on Nov. 7, 1972, after community leaders concluded that the only way to save a deteriorating downtown was to find a magnet that would anchor the northern edge of town as Bush Memorial Stadium already had on the southern end, with its premanent residents, the football and baseball Cardinals.

But construction was threatened when inflation brought the price tag to more than $35 million, and it was the local business community that saved the project. August A. Busch Jr., head of the brewery firm here that bears his name, raised $3.5 million from local firms - starting with $500,000 from St. Louis-based Monsanto Co.

Monsanto Chairman John Hanley said the chemical firm considered its "gift" an "investment in its home town and in the city where its world headquarters is located."

And local labor leaders, in a city known previously for construction strikes, pledged no work stoppage. Ground was broken in April 1974, and the first big convention here was held last June - that of the National Association for the Advancement of Colored people, which drew 8,000 visitors - filling 6,500 hotel rooms within walking distance of the complex and some suburban hotels as well.

On all sides of the new center, meantime, St Louis businesses are investing in major redevelopment projects. Eight firms have invested in a Convention Plaza Redevelopment Corp., which plans to construct in the next decade hotels, office buildings, shops and parking garages.

Companies involved are Anheuser-Busch, Bank of St. Louis, First National Bank of St Louis, Mercantile Bancorporation, Southwestern Bell Telephone Co. (a unit of American Telephone & Telegraph), the department store firm of Stix, Baer & Fuller, Union Electric Co., and Sverdrup Corp., a development firm.

The first effort of the multi-million-dollar program - a $20 million, 620-room Sheration hotel - recently opened next to the convention center. Pedestrian skywalks and bridges will connect parking garages with new buildings, malls and such existing retail stores as Stix. Baer and Famous-Barr (flagship of the May Department Stores Co., owner of the Hecht Co. in Washington)

Beckerle, engaged in the convention business here since 1966, said the convention center is obviously the key to this downtown rebirth, and he forecast that the center will be expanded within a decade. Already it is the tenth largest such facility on the continent with a total of 436,000 square feet.

According to Beckerle, big exhibition space is the key to his business for the next decade or so. Every major group with associate exhibits and product demonstrations wants to travel to the four regions of the country in rotation - and only the biggest centers in each region will get the business.

An American Newspaper Publishers Association production convention here next June will attract 1,300 separate exhibitions compared with 150 some 15 years ago. And the convention To install the booths, 700 St. Louis will draw an estimated 12,000 persons workers will be hired.

It is this type of meeting which cannot be held in Washington without a large convention complex, Beckerle said. At the same time, the proposed D.C. center is "way overpriced," he added.