At 2:45 p.m., in front of the Capital Hilton hotel on Sept. 21, a tour bus will board 40 very important visitors and their Washington area hosts for a combined bus and subway tour of the District of Columbia.

It will signal the start of the most aggressive campaign in Washington history to attract companies, trade associations and jobs to the local economy.

Although the Washington area already has one of the most stable and affluent business environments anywhere in the late summer of 1978, local leaders are counting on continued population growth to provide further economic gains in future years.

Washington is one of the nation's few large urban areas projected to grow significantly between now and 2000 but the potential for slower growth in federal government employment is considered real in an age of taxpayer revolt. Thus, there is a new emphasis on building a strong non-government business base to Washington - which was the goal of original local booster and Northern Virginia resident George Washington many years earlier.

Under the title of "Executour," the Metropolitan Washington Board of Trade is bringing 40 top executives from outside businesses to the D.C. area, for a first-hand demonstration of the local business environment. For each visitor, there will be a Washington business executive as host.

For two days, at the expense of local businesses, the visitors will be wined and dined, entertained and informed about the Washington area. Separate bus tours and presentations are planned in the city, Northern Virginia and the Maryland suburbs.

Acting Gov. Blair Lee of Maryland, Lieut. Gov. Charles Robb of Virginia and D.C. Business and Economic Development Director Knox Banner will make separate pitches for their jurisdictions in a program that emphasizes the attraction of the metropolitan area as a whole.

There will be dinner and a performance at the Kennedy Center, speeches and a panel discussion featuring some newcomers who will explain "Why we're in Washington."

Although several suburban counties have been engaged for years in successful development programs to attract business and jobs, the concept of promoting the entire area was started by the Board of Trade only since the mid-1970s. The District government, meanwhile, began a development program in earnest only during the past year.

Previous programs of the Board of Trade have included publications and visits to other cities as well as providing information and guidance to outsiders upon request.

While these efforts helped convince some groups and businesses to move here, most significant relocations of jobs to Washington in recent years developed because of other factors.The location of the federal government and its pervasive role in the economy have convinced many business executives that they should live and work close to decision-makers. Business expenses and taxes - less here than in some urban areas - have brought about some moves. And the relative affluence of most area residents has been attraction enough for others.

However, according to Board of Trade Executive Vice President John Tydings, his group's "Case for Washington" program has been a key factor in the decisions of 26 firms and associations to move here or open major area facilities since February 1977. These "successes" represented 2,700 new jobs and whetted the appetite of growth-minded local business leaders for an expanded effort to promote even more relocations.

More than $80,000 has been contributed to the second phase of the Board of Trade program and another 70 promising leads and prospects are being developed, according to officials of the group. Such diverse publications as the Financial Times of London, Dun's Review, Engineering News Record and the New York Times recently have printed articles about the new economic boom here, fueled by Washington's attraction as a place to live and work.

Business executives who take advantage of the Board of Trade's promotion campaign will listen to optimistic assessments of the Washington environment at a time when most economic indicators here are upbeat:

Corporate profitability for major firms is at record levels in many instances. For example, Marriott Corp., engaged in food services, hotels and airline catering, last week posted a 30 percent increase in fiscal year earnings and an even larger increase for the most recent quarter; the firm employs some 14,000 area residents.

Stock prices of public companies in the Washington region, on average, have been increasing steadily all year while Wall Street otherwise has been on a rollercoaster.

Areawide retail sales for the first six months of 1978 rose an estimated 13 percent from the same period last year for a total volume of some $5.7 billion, somewhat higher than a national average gain of 9 percent.

Unemployment in the area has remained significantly below national averages throughout 1978; in July, the seasonally adjusted jobless rate here was 4.7 percent compared with 6.2 percent nationally. Some 30,000 jobs were added to the area economy in the past year - mostly in retail or wholesale trade, services and construction. Area employment is projected to rise to 1.8 million in 1985 from under 1.6 million today, averaging 2.4 percent annual growth.

Construction is booming with $748 million of new building started in the first six months this year compared with $715 million in 1977, when annual volume set a record $1.6 billion.

The subway system will begin Saturday and night service until midnight (instead of closing at 8 p.m.) later this month, which is expected to increase business volume at stores, restaurants and entertainment complexes near entrances.

New data from Sales and Marketing Management magazine pinpoints the local area as the most wealthy among the nation's major urban centers, with the highest per capita spendable income ($7,984 per man, woman and child in 1977) and a 155.5 percent growth in per-household spendable income over the last decade.

In general, the consensus of local business leaders is that economic statistics will continue to show gains during the fall and winter. Retailers, in particular, are looking for a better performance between now and Christmas.

Sheldon Fantle, president of Peoples Drug Stores, sums up the consensus viewpoint: "On balance, I feel that the last half of the year will be fair-to-good, with moderate growth in volume and limited increases in corporate profit due to the escalating costs of doing business on a day-to-day basis."

Balanced against the long list of glowing statistics about the local economy are arraigned some real problems often overlooked. Consumer prices here, for example, have been growing in 1978 at a rate that exceeds the national average and have accounted for more than half of the increased retail sales volume; food store prices alone spurted 3.2 percent from May to July.

As a result of the adverse impact of inflation on spendable income, consumers are described as very cautious. Department store spending has been sluggish as Washingtonians concentrate on necessities.

In addition, unemployment remains a serious problem in the District, if not the suburbs. Statistics published last week showed D.C. unemployment at 9.6 percent in July and black teenage joblessness in the city for the summer was estimated at 50 percent.

According to the D.C. Department of Labor, the area jobs trend shows an increasing number of "white collar" jobs, with most future growth in clerical, professional and technical positions. These sectors of the job market require greater attention to training unemployed persons here for such skills or new attention to attracting light industry or manufacturing, for which Washington never has been a major center.

And a new U.S. Chamber of Commerce forecast says that economic conditions in D.C. will be worse through 1980 than in the Maryland and Virginia suburbs, with an actual decline in the city's employment base.

Board of Trade President R. Robert Linowes has emphasized that although Washington is enjoying prosperity, "there is no time for euphoria."

Even as the D.C. area is coming of age, business leaders must not ignore these problem areas, Linowes says: continued unemployment in the city, a need for low income housing and potential water supply problems.

"Poverty and frustration cannot long co-exist with affluence. Either we take the lead (in solving the problems), or we will be forced to deal with the consequences," Linowes argues. "We must forego the tendency to stay in our small selfish business world. Now, more than ever, we as business people must think of our function and that function means becoming involved in the political and social issues of our time."

As the Board of Trade is about to launch still another drive to attract other businesses to Washington, the message from that organization's president seems to be this: Welcome to Washington's wealth and prosperous business environment, and please help solve the serious housing and employment problems that exist here.