Mamas, don't let your babies grow up to be farmers -- times are hard, and now Willie Nelson is making another effort to help out. A second Farm Aid concert, to be combined with the country singer's traditional Fourth of July picnic, has tentatively been given the go-ahead, according to a spokesman for the Texas Department of Agriculture, which will sponsor the fundraiser.

Farm Aid II will be held in Memorial Stadium at the University of Texas in Austin; Nelson and Agriculture Commissioner Jim Hightower plan to announce an agreement with the university and provide further details about the concert in about two weeks. The original Farm Aid concert last September raised about $9 million in donations to help financially troubled American farmers.

Deleting McGovern

Most references to George McGovern's failed effort to become president of St. John's College in Annapolis were deleted in the April issue of The St. John's Reporter, the school's alumni publication. The Baltimore Evening Sun reported yesterday that Edwin J. Delattre, the college's outgoing president, recalled nearly all of the 7,000 copies of the publication. The Reporter's original headline included the subhead "McGovern Loses Bid," which was eliminated in a revised edition.

"It's a simple matter," Delattre said yesterday. "The lead article intended to announce the election of the new president . . . There were a number of things in the article about the search process and they were a distraction . . . It was inappropriate; it was a breach of confidence, and because of its incompleteness, it was highly misleading." Charles E. Dunn, vice president for college advancement, said reprinting the paper cost the school about $750.

Amy Carter's Speech

Amy Carter, who was arrested last month for participating in a demonstration against IBM's South African business dealings, spoke last night at the Washington Convention Center about South Africa and her antiapartheid work at Brown University, where she is a freshman. The daughter of former president Jimmy Carter spoke at the National Rainbow Coalition convention, along with the Rev. Jesse Jackson, Del. Walter Fauntroy, Rep. William Gray and actor Robert Blake.

End Notes

Pianist Vladimir Horowitz, who has returned for a visit to his Russian homeland for the first time in more than 60 years, turned a rehearsal into a full-scale concert yesterday. Students from the Moscow Conservatory packed its Rachmaninoff Hall to hear Horowitz, 81, rehearse for his concert tomorrow. Horowitz gave three requested encores before waving goodbye to his audience with his handkerchief. The pianist arrived in Moscow Monday . . .

Frank Sinatra apparently approves of President Reagan's attacks on Libya. The singer said he sent Reagan a telegram that read simply, "Encore, encore, encore. Francis Albert" . . .

Mayor Marion Barry will speak at a benefit for the Committee for the Bishop Desmond Tutu Southern African Refugee Scholarship Fund tonight at the Sheraton Washington, and Naomi Tutu Seavers, Bishop Tutu's daughter, will relay a message from her father. The benefit, cosponsored by the Fund and the Capital City Chapter of the National Coalition of 100 Black Women, will present its first annual "Woman of the Year" award to Mary Frances Berry, commissioner of the Equal Employment Opportunity Commission . . .

A turn-of-the-century "love chair" that was reportedly used by King Edward VII when he was prince of Wales will go on sale tomorrow at Drouot, an auction hall in Paris. The chair is made of sculpted wood with two metal stirrups on either side and was reportedly part of the furnishings in one of the rooms at Chabanais, a famous brothel frequented by the prince. The chair is valued at $14,280 to $17,140.