Mixed emotions.

That's the best way to describe how executives at Calvert's Social Investment Fund in Bethesda feel about their decision to go from being an old-fashioned no-load, no-commission fund to a fund that levies a 4.5 percent sales charge.

That decision might sound mundane, but in the case, the change is equivalent to finding out that the young man you knew as a flaming campus radical, in blue jeans and a slogan-painted T-shirt, is now pursuing life on Wall Street in a three-piece business suit.

Like the young man, the Social Investment Fund has joined the Establishment -- or at least the trend. These days, there are fewer and fewer pure no-loads or backend loads. A back-end load is a withdrawal charge.

The new sales charge will apply, it should be noted, only to the fund's Managed Growth Portfolio, not to the Money Market Portfolio.

When the Social Investment Fund was organized more than three years ago, it was built around the idea that it would carefully screen its investments. Specifically, the fund does not invest in companies that pollute the air or water, build weapons systems, discriminate against women or minorities, produce nuclear power or do business in South Africa.

No wonder they called it a "do-gooder" fund.

With those kinds of lofty, noncommerical objectives, it is no surprise that the men who started the fund also firmly believed in the idea that no-load funds were better for investors than funds with sales charges.

It was not easy for them to change that way of thinking.

"We struggled with the load idea," said D. Wayne Silby, president of the Social Investment Fund. He and a college friend, John G. Guffey, president of the Calvert Group, started Calvert in 1976 and opened the Social Investment Fund in late 1982.

"The idea of putting a load on it offended my sense of good value, of getting a good deal," said Silby.

Guffey, too, worried about the change. "We have agonized over it for the last year," he said. Guffey worried especially that the change might create adverse publicity -- and that the fund would not be considered "as pure as before."

What finally pushed them over the line, Silby and Guffey said, was the feeling that it was time to seek a wider audience for the Social Investment Fund, which has $60 million in its equity portfolio and $54 million in its money market portfolio.

They felt there were many people who would invest in the fund if they knew about it or were told about it.

That meant Calvert had to make it possible for brokers to sell the fund by allowing them to earn a commission on the Managed Growth Portfolio. So they established a 4.5 percent commission, which will go into effect in July. the brokers also will earn a small regular fee on the amount of money their clients have invested.

One factor that helped persuade Calvert officials to make the change, Silby said, was the number of requests they had from brokers who said they had clients interested in social investing but had nothing to sell them.

Silby said that after much soul-searching he finally concluded there wasn't anything wrong with letting brokers earn a reasonable commission for bringing in new investors.

"We don't want to be spinning around in our own circle," he said. "We want to become part of the mainstream."

Did that mean that Silby, a 37-year-old-lawyer, entrepreneur and futurist, had changed his philosophy about no-load funds?

"I had my concerns," he said, "but I decided, let's swim where the water is going. . . . My thinking is now more results-oriented."

From Guffey's point of view, adding the sales charge will make it easier to buy advertising space to compete with T. Rowe Price Associates of Baltimore in the pension investment area and with the Dreyfus Third Century Fund of New York in the social investment category.

One of the other persuasive factors is that Calvert has considerable experience usising an outside sales force for some of its other financial products. Its year-old Washington Area Growth Fund is being sold by brokers. Calvert counts $1.85 billion in all of its fixed-income and equity funds.

Because Calvert is owned by the Acacia Mutual Life Insurance Co. of Washington, the Social Investment Fund also will have a ready-made sales force in the 300 Acacia agents who have been licensed to sell securities. Many of the major brokerage houses are expected to sell the Social Investment Fund.

Wayne Bardsley, a senior vice president at Calvert, believes that broker network could take the Social Investment Fund to $150 million to $200 million by the end of the year. "We've really only scratched the surface of the market," he said.

The brokers, Bardsley believes, will help spread the message that "you don't have to give up financial returns to feel good about where your dollars are going."

Actually, the performance of the two portfolios in the fund has been competitive but not all that unusual. In 1985, the Managed Growth Portfolio rose 26.8 percent, compared with a 27.6 percent average for growth and income funds and a 27.2 percent average for equity funds, as measured by Lipper Analytical Services. The Money Market Portfolio was up 7.8 percent in 1985, compared with 7.7 percent for Donoghue's Money Fund Average.

What is unusual about the fund is the lineup of 53 companies that make up the Managed Growth Portfolio and the way they are described in the portfolio list. Here are some examples.

*Allegheny Power System, New York. "It neither owns their owns nor operates nuclear power plants, deriving almost all of its power from coal-fired plants."

*Bell Atlantic, Philadelphia. "Approximately 70 percent of Bell Atlantic's 80,000 employes are represented by unions. . . ."

*First Virginia Bank, Falls Church. "First Virginia has no foreign loans, indicating that it is neither supporting repressive foreign regimes nor exporting capital."

*Herman Miller Inc., Zeeland, Mich. the company has been consistently innovative in designing people-oriented work environments."

*Stride Rite Corp., Cambridge, Mass. "The company operates two day-care centers serving employes and neighborhood children."Clearly, in this fund, the portfolio managers are looking for stocks that can achieve a high level of performance but also can pass a special set of tests for social objectives. That obviously makes the stocks harder to find.

The interesting thing is that three years ago, brokers probably wound't have been interested in trying to sell a social investment fund. But much has happened since then to strengthen the concept, including the protest over apartheid in South Africa.

The Calvert slogan is: "Put your money where your heart is." Under Calvert's new broker distribution system, many more investors are likely to get a chance to do that, even if it costs more than before.

There'll be a new bank in town soon. It'll be called Federal City National Bank and it will be at 555 New Jersey Ave. NW. Headquartered on Capitol Hill, it will serve the Washington area.

Its founder is attorney Charles Emmet Lucey, former chairman of Century National Bank of Washington. The president is James F. Whelan, a life insurance and banking executive. Fourteen other Washington-area business people are listed among the organizers, directors and officers.

The bank is being launched with a new stock offering of 350,000 shares at $10 a share, for a total of $3.5 million, before expenses. Of the 350,000 shares, 35.4 percent will go to the organizers, directors and officers, 64.6 percent to the public.

An offering circular may be requested by writing to Federal City National Bank, P.O. Box 75038, Washington, D.C. 20013-5038.