Commodity interests will have some new advocates and regulators here soon.

The Chicago Board of Trade will unveil its proposal for expanding its office here at a membership meeting today. President Robert K. Wilmounth confirmed. He declined to detail the plan in advance, but confirmed that the exchange will continue to be a client of Washington attorney Tad Davis.

In a recent Midwest speech, Wilmouth said the CBOT would hire an experienced, full-time lobbyist for Washington soon. He added that he had "a man in mind," but would not disclose the name.

This week Capitol Hill and industry sources said Michael McLeod, general counsel and staff director of the Senate Agriculture Committee, plans to leave the committee April 1 to join Davis' firm.

McLeod confirmed that he is considering leaving the committee for private law practice. He has held the powerful role of right-hand man to Chairman Herman Talmadge (D-Ga.). McLeod said his plans won't be completed until next week, but stressed that he would not undertake any lobbying on the Hill in his new position.

McLeod intends to leave as soon as the next farm bill is reported out, sources said.

The staff director had been interested in replacing William T. Bagley as chairman of the troubled Commodity Futures Trading Commission until late last year when Bagley was turned down for a California state judgeship that he had sought. Hill sources said Talmadge also was extremely cool to the idea of his chief aide leaving to head a controversial agency like the CFTC.

Meanwhile, David Gartner, former administrative assistant to the late Sen. Hubert Humphrey (D-Minn.), is expected to replace CFTC Vice Chairman John V. Rainbolt II May 1, although Rainbolt reportedly would like to delay the changeover until June 1.

White Huse and Senate sources report that the renomination of CFTC Commissioner Read Dunn Jr., which was thought to be assured, is in jeopardy.

While Dunn is supported by southern congressional delegations, the White House and some vocal congressmen are pushing to free that position for a more prestigious regulator, possibly from the Securities and Exchange Comision, or a prominent attorney as a sign that the administration is serious about "reforming" the commission. While half a dozen names have been suggested as nominees, no leading contender has emerged yet, sources said.