On one side is Joe L. Allbritton, an aggressive investor who learned the ways of business in Texas banking and became one of the richest men in the United States today, with a net worth estimated at well over $100 million.

In the other corner are the 25 directors plus assorted officers of Riggs National Bank, whose major goal when the new year began was a smooth beginning for the bank holding company they planned to establish.

These are the unlikely opponents in what is becoming the most bitter corporate take-over fight here in more than a decade.

And this fight has cut deeper into the roots of Washington business than takeover bids in earlier decades because 145-year-old Riggs is the area's largest financial institution and reflects the Washington establishment in its base of customers, owners and directors.

To date, the confrontation has been conducted in the form of rather gentlemanly communications to the individuals and institutions that own Riggs commons stock (3 million shares outstanding, of which 15 percent already is owned by Allbritton).Allbritton has made an offer at $67.50 a share for at least 600,000 shares. That would give him 35 percent of Riggs stock.

Riggs has said the price is too low, while suggesting that a rival bid is in the works.

Other than these official pronouncements from both sides, Allbritton and Riggs have declined to explain what is happening or why.

Why is Allbritton suddenly moving to gain effective control of the largest bank in the nation's capital?

Why do Riggs directors object?

What bank has agreed to loan Allbritton upwards of $50 million to buy Riggs stock"

What type of bank does Allbritton want to control -- a regional business bank, an international giant, a consumer-oriented institution?

Would he become chairman and dismiss current officers?

What difference does it make who owns control of Riggs?

These are just several of many questions that seem legitimate to the community of Washington, where Riggs is a formidable power -- a $3 billon institution that locally is one of the largest consumer and business lenders and owns a major area credit business, Central Charge Service.

Vincent C. Burke Jr., the normally genial chairman of Rigs and a long-time Washingtonian, has been designated by the bank board as the one and only spokesman for their interests. But he has declined to talk to reporters since the morning of Feb. 9, when Allbritton revealed his surprise attack. Allbritton makes statements only through a spokesman or the New York public relations firm of Hill and Knowlton.

The next mimeographed statement on Hill and Knowlton letterheads may be an announcement about how many shares of Riggs stock have been tendered to Allbritton so far. Although his offering does not expire until March 10, he had said that if 600,000 or fewer shares were promised by last Wednesday night, he would take them all. If more than 600,000 shares are offered, he will buy them on a pro rata basis. Or he has said he may decide to buy any amount tendered.

Another announcement should come early this week, revealing whether the federal government needs more time to study potential antitrust questions in Allbritton's proposed acquisitition. He is chairman of the holding company for University State Bank in Houston but has disposed of other bank investments.

Finally, every Riggs investor is waiting for an announcement from the bank's management or its own New York agents. Will there be a rival bid at a higher price?

Stock analysts said that an opposing bid to Allbritton probably would be pegged at $72 to $75 per share for a stock that was trading under $40 last summer. That would put the ball in Allbritton's court, and there is some speculation Riggs could soar to $90 a share in a game of can-you-top-this.

One Washington investment officer noted that Riggs' management, "with all the bank's dignity" well-established in their thinking, probably had relied on the notion of stock-holder loyalty to carry it through any challenge. But times have changed, and "I'm not convinced you can depend on stockholder or product loyalty . . . There's not much loyalty anywhere," this Washingtonian said.

Allbritton's aims are the subject of intense speculation, but that's all. One person describes Allbritton's record as that of a "hand's-on, not-passive investor who gets involved," and this source chastized Riggs officers for being "naive" about his intentions. But another person, close to Allbritton, tells a different story.

After he purchased and then sold The Washington Star in the 1970s, Allbritton began buying Riggs stock over a period of time. Burke reportedly was informed ahead of time in every instance.

In addition, Burke and other Riggs officers were kept well-informed when director Jorge Carnicero decided to sell his large interest in the bank to Allbritton. That sale took place in January. On the surface, Allbritton and Riggs had begun peaceful coexistence.But something happened.

According to the assessment by the source who knows Allbritton, he decided some time ago to adopt Washington as his home, even though some persons here consider him an outsider. He maintains an office in Houston and frequently travels there, but his full-time home is here, as is his Allbritton Communications headquarters which owns newspapers and television stations (including WJLA, Channel 7).

He is said to like Washington. He wants to be a part of its business, cultural and social community. He repeatedly complains that the public doesn't understand that he was forced to sell The Star by a Federal Communications Commission decision on multimedia ownership here.

At first, this assessment goes on, Allbritton was said to be interested in Riggs only as an investment in a major local business. He had no desire to become part of management or the principal owner. But he did want to increase his holdings above the 15 percent level he attained when Carnicero's stock was purchased -- at least to about 25 percent.

A vote by most Riggs directors in January that it would not be in the best interests of the bank for any individual to own more than 15 percent may have been seen by Allbritton as more than a challenge to him: a slap in the face, informants said.

Whatever the cause of Allbritton's decision, and whatever the reasoning of Riggs' directors in trying to stop him, Riggs has a challenge.

According to the bank, Allbritton faces interest costs of $14 million a year on the bank loans he has arranged to buy Riggs stock. As one area banker said: "Who around Washington can carry that kind of cash flow?" in mounting a rivalry with Allbritton. The banker said he didn't know anyone to fit those financial measurements.

And if Riggs brings in an outside group, what difference is there between those investors and Allbritton? At least he lives in the District.