Ronald Reagan earned more than half a million dollars in 1979, most of it from speeches, and paid nearly half of it in federal income taxes.

Abandoning a longstanding practice of treating his financial affairs as a private matter, Reagan today made public his 1979 federal tax returns. They showed he had earned income of $515,878 and paid taxes of $230,146.

The 23-page tax return was issued here by the Reagan for President Committee without comment while the Republicans nominee was attending a meeting with advisers in his Pacific Palisades home.

In Washington, Reagan's director of communications, Joe Holmes, said the former California governor's decision to make his income taxes public was a result of continuing press requests for the California, coupled with an awareness that President Carter had made his tax returns available.

"Governor Reagan still has strong feelings about his privacy, but he and his advisers felt he had nothing to hide, so he did it," Holmes said.

What the return revealed, perhaps more than anything else, was Reagan's personal reason for delaying the announcement of his candidacy until late last year -- the last possible moment. After he became a candidate for president Nov. 13, 1979, Reagan gave up his three primary sources of income -- speaking fees, a radio commentary on 200 stations and a weekly newspaper column.

The tax return showed that Reagan made $380,500 from his speaking engagements, $58.453 from his radio broadcasts and $26,757 from the newspaper column for a gross income of $465,710 from personal services. He had $166,733 in expenses in this category for a net speaking and writing income of $298,977.

The largest expense items were $55,548 in professional services and $47,517 in salaries, both of these presumably paid to the Los Angeles advertising firm of Deaver and Hannaford, which contracted for the column and radio broadcasts and for many of the speeches.

Reagan's other major categories of income were $90,394 from interest payments, $93,809 from capital gains $23,754 from dividends, and 17,600 from pensions and annuities.

The capital gains were from stock Reagan sold between March 29, 1979, and July 13, 1979. Most of the stocks were purchased after 1974, when Reagan completed two terms as California's governor, at a total cost of $720,399. He sold them for $953,975, giving him a profit of $234,455.

The largest portion of this gain came from a single block of stock -- 11,000 shares of Continental Illinois Properties -- which Reagan sold for a profit of $203,099 on July 11, 1979. Continental Illinois Properties is a real estate investment firm.

Reagan realized $18,614 in profits from the sale of 2,000 shares of Dart Industries common.The company is owned by justin Dart, one of three trustees of the Ronald Reagan Trust and a fund-raiser for Reagan's gubernatorial and presidential campaigns.

William French Smith, Reagan's personal attorney and another of the trustees, said that the decision was made eight to 10 months ago to sell all of Reagan's stock "because it was good from an investment standpoint and because he was declaring his candidacy."

Smith said that all of the Reagan stock owned by the Reagan Trust has been disposed of except for 3,000 shares of Cowles Communications stock, which Smith said he expects to be sold soon. Reagan's holdings are in a blind trust and he does not participate in decisions affecting them.

The nearly $1 million that was received from the stock sales has been put into high-interest-bearing savings accounts, Smith said. He said the interest on this money and the money Reagan receives from his governor's pension (about $15,000 this year) will be Reagan's only earned income in 1980.

The tax return also revealed the limited nature of the farming operation on Reagan's hideaway 688-acre ranch north of Santa Barbara, which he purchased in 1974 at a cost of $526,000. The value of the ranch, also owned by the Reagan Trust, has been estimated at up to $2 million.

The ranch has been sheltered from most taxes as an agricultural preserve since 1971, three years before Reagan and his wife, Nancy, purchased it.Reagan pays property taxes of $862 a year. He would pay taxes of $42,000 a year if it were not an agricultural preserve.

This farming operation that qualifies the ranch for this tax break, according to the income tax return, is limited to "14 steers" that graze there. aReagan showed a net loss of $9,105 on his farm operation in 1979.

The Reagan tax return showed him paying a far higher percentage of his income to the government than has President Carter. Reagan's advisers believe it shows their candidate in a good light.

It is a far cry from 1971, when a Sacramento television reporter was tipped that Reagan had paid no state income taxes in 1970. Reagan, then fighting against state income tax withholding under the slogan, "Taxes Should Hurt," acknowledged that he had paid no taxes because of "business reverses."