Michael K. Deaver, the public relations man and former White House assistant who has turned his connections with Ronald and Nancy Reagan into a multimillion-dollar business, has a new $500,000-a-year client: the Royal Kingdom of Saudi Arabia.

Deaver is the man whose recent lobbying of the Office of Management and Budget on behalf of the B1 bomber, manufactured by one of his clients, has given new moment to concerns that the door between the White House and Washington's lobbying industry is revolving with too-dizzying speed.

According to a formal contract filed last month with the Justice Department, Deaver will "provide advice and consultation as to ways to strengthen American understanding of and respect for the Kingdom of Saudi Arabia." Deaver "may on occasion" communicate on behalf of the Saudis with members of the executive branch and of Congress, and will be responsible for "tracking and analysis of trade trends, policy initiatives and developments in Washington which may materially affect Saudi Arabia's economic interests," according to the contract.

The deal -- half a million a year plus expenses, payable quarterly in advance -- was formally made between Saudi Arabia and Michael K. Deaver & Associates, Deaver's firm, which he is in the process of selling to a London advertising and public relations firm for $18 million, though he will continue to run it. However, the Saudis stipulated in their contract that Deaver personally will "act as principal officer for the matter." If Deaver ceases to be active in the firm, the Saudis can cancel the contract.

Deaver wouldn't comment, but William F. Sittmann, a vice president of his firm, sort of commented. "If the Saudis want to discuss it they are capable, but we won't discuss contracts," he said. No Saudi Embassy spokesman could be reached for comment.

The Deaver deal gives the Saudis a Republican agent in Washington. For years they have had a Democrat -- Frederick G. Dutton, a Californian and veteran of John F. Kennedy's New Frontier who practices law here with his wife Nancy. There's plenty of business to go around. Nancy Dutton said last night that "we are the lawyers for them. Deaver is no lawyer," she added.

Among Deaver's other foreign clients are the governments of Canada, Mexico, Singapore and South Korea.

King of the Forest . . . In a bid to honor California's favorite son, the Los Angeles County Board of Supervisors has voted to change the name of the Angeles National Forest to "Reagan National Forest," and has directed L.A.'s lobbyist here to drum up support for the necessary legislation.

The Sierra Club, highly critical of the president's record on the protection of natural resources, has reacted with swift alarm, calling the move "an April Fool's joke on the people of California."

"It's absurd," said club spokesman Bob Hattey. "Substantive issues aside, naming a national forest after Ronald Reagan is like naming a day-care center after W.C. Fields."

Supervisor Pete Schabarum, who introduced the motion which the city's governing body passed on a unanimous 4 to 0 vote, said the more than 8 million people in Los Angeles County have a "special feeling" for the president, and that "recognizing his special love for the outdoors" would be an appropriate act by members of Congress.

Promises to Keep . . . Barely a month into his new post, Agriculture Secretary Richard E. Lyng is out of town today -- making a quick tour of Iowa and Nebraska in payment of a political debt.

Lyng's two days of tours and talks with farmers were promised to Reps. Virginia Smith (R-Neb.) and James Lightfoot (R-Iowa), who are "hosting" the trip, when Reagan asked their support last month for his $100 million bill seeking aid to the Nicaraguan rebels.

Said a Smith spokesman, "We wanted to give the new agriculture secretary a first-hand view of what is happening in the heartland at planting time."

And perhaps to give the heartland a first-hand view of the agriculture secretary prior to election time. From news services and staff reports