President and Mrs. Reagan paid more than $20,000 in back taxes and interest to the federal government and the state of California last year after the Internal Revenue Service disallowed claims on their 1978 and 1979 returns of business losses in the operation of their Santa Barbara ranch, their tax lawyer confirmed yesterday.

The lawyer, Roy D. Miller of Los Angeles, contended that the disputed claims had been permitted in previous years but were rejected by the IRS for 1978 and 1979 after an audit that began in mid-1980 when Reagan was running for president.

Miller confirmed a "ballpark" estimate that the Reagans were required to pay about $20,000 to $22,000 plus 12 percent interest. The interest payment of $2,734 was taken as a deduction on the Reagans' 1981 return, which was made public last month.

Miller said he could not recall all of the details of the disallowed expenses claimed in connection with operation of Rancho del Cielo, the Reagans' mountaintop vacation retreat 29 1/2 miles northwest of Santa Barbara.

At the time Reagan made public his 1979 tax return, news accounts reported that he claimed a loss of $9,015 on his ranch. The articles said that he reported income of $3,024 from the sale of 14 steers and $3,350 from unspecified "rents" but that these were more than offset by expenses. They included $3,839 for labor, $598 in feed, $367 for horseshoes, $1,422 in gasoline and $1,118 for utilities. Other deductions included $15 for depreciation of a fan used at the ranch.

Reagan reported income of $515,878 for 1979, more than half of which went for taxes, including $230,886 in federal income taxes and $32,050 in state and local income taxes, according to the news accounts.

Meanwhile yesterday, deputy White House press secretary Larry Speakes said the White House will reprimand anyone who gives Reagan a gift and then uses the resulting thank-you note to promote a business.

"When matters of this type are called to our attention . . . they receive a pretty stern letter from the White House counsel indicating that we don't look with favor on them using the president's name," Speakes said.

White House counsel Fred Fielding said later that such letters would be sent to a Reno, Nev., belt buckle manufacturer and a Mechanicsburg, Pa., jeweler who told The Post that they had given the Reagans gifts with the idea of publicizing their products.

They were among a group of 47 friends, manufacturers and strangers who gave the Reagans thousands of dollars in jewelry, sculptures, crystal, sweaters and shoes in their first year in office. The Reagans' 1981 financial disclosure form indicated that the total value of the gifts was more than $31,000.

In a related matter yesterday, Nancy Reagan's office announced that she will return a diamond necklace and a pair of diamond earrings worth several hundred thousand dollars to the Harry Winston Co., a Fifth Avenue diamond merchant.

Ronald Winston, the firm's president, has said the diamonds were given so they could become the "nucleus of an ongoing collection for first ladies of the White House."

But an administration official, who said Saturday the White House did not feel it was proper to keep the Winston jewels because of a feeling "that there shouldn't be state jewels," said they would be returned.

The announcement by Mrs. Reagan's office said the jewels, on loan to her since inaugural festivities 16 months ago, would be sent back after she and the president return from the state visit to Great Britain and Europe next month.

David Waller, senior associate White House counsel, said Reagan has no recollection of meeting Rex Cauble, a 68-year-old Texas millionaire rancher-businessman who gave the president two pairs of boots worth $600 on behalf of himself and the American Footwear Industry Association of Dallas and received presidential thank-you notes.

Waller said he thinks Cauble is a member of a national horse riding club called the Rancheros to which the president belongs.

Since he gave the gift last June, Cauble has been convicted on federal charges of conspiracy, embezzlement and racketeering and sentenced to 10 five-year terms. Prosecutors said Cauble financed and profited from the "Cowboy Mafia," which smuggled 106 tons of marijuana from South America in 1977 and 1978.