President Reagan's oldest son is under investigation by state and county officials in California for allegedly diverting funds invested in a gasohol development project to support his travel during his father's election campaign.

The Los Angeles Times reported yesterday that Michael E. Reagan, 35, was being investigated by the Los Angeles County district attorney to see if he misused $17,500 given him by four friends who invested in a venture of his called Argicultural Energy Resources, a firm Reagan started last year to procure alcohol for use as a fuel additive.

Sources in the district attorney's office said investigators are seeking to determine if Reagan spent the money on travel during his father's 1980 campaign or whether the four investors gave him the money to be used on expenses incurred during the campaign, an action that might be construted as an illegal campaign contribution.

"I want to emphasize that nobody has been charged in this case," one source in the district attorney's office said. "This matter is still under investigation."

The district attorney's office confirmed that it also is investigating whether Reagan sold shares in AER without a license.A Jan. 12 memo written by Alan S. Weinger, counsel for the state's Department of Corporations, indicated that Reagan had not registered his firm with the department as required by law and did not have a state license to sell securities.

"It is this writer opinion that Reagan violated Section 25110 of the corporate securities law when he offered and sold stock to investors," Weinger wrote in his memo. "The offer and sale of stock in AER has not been qualified with this office and there do not appear to be any exemptions available for these transactions."

"It's like they're trying to find me guilty of something, no matter what it is," Reagan said at his Sherman Oaks home.

"I don't believe they'd be doing this if my name was Jones."

Reagan's attorney, Donald Wager, said he wrote Los Angeles District Attorney John Van de Kamp expressing surprise at the allegations.

"In this letter, all the investors have expressed dismay that the district attorney is investigating AER," Wager said. "They don't think he has done anything wrong, there has been no misuse of funds. Mr. Reagan started AER as a sole proprietorship; nobody ever thought it was a corporation, and in May of 1980 all the appropriate papers were filed by his lawyers."

Most of the information published by the Los Angeles Times yesterday was contained in two affidavits filed by the district attorney's office to get two search warrants -- one to obtain documents at Reagan's home and the other seeking documents in a Hollywood branch of the Pacific National Bank where Reagan has an account.

The district attorney's office confirmed the search warrants were obtained last Friday and documents pertaining to the formation of Reagan's enterprise and the disposition of invested funds had been taken. Examination of those documents has just begun, a source indicated