LOS ANGELES (AP) _ Economist Arthur Laffer, whose theories were instrumental in the development of ''Reaganomics,'' says his GOP Senate campaign has gone broke.

But Laffer said he remains optimistic about his campaign.

When he announced his candidacy in July, Laffer said he planned to raise $2.5 million, with $1 million going for overhead and the rest for advertising.

At the time, his chances looked good in the crowded field of 12 seeking the Republican nomination for U.S. Senate in the June 3 primary.

He had nationwide name recognition: Laffer's economic curve theory was a cornerstone of the Reagan administration's economic policies.

Laffer received $1 million in contributions - more than all but two of his rivals, but considerably less than his goal. Laffer bumper stickers, buttons and T-shirts were printed, but there have been no Laffer radio or television ads.

And this week his campaign reported a net debt of about $23,000.

''Issues are not my problem, raising money is not my problem, managing campaigns ... is something I can learn,'' he said.

One of his biggest mistakes, the 46-year-old candidate said, was making fund-raising tours outside California.

Laffer went to New York, Connecticut, Ohio and Puerto Rico. While he was gone, political organizations and the media were beginning to turn toward the Senate race and his competition.

''I overextended labor on fund-raising,'' he said. ''I could, if I had to, spend one or two or three days less on trips back East.''

When in California, Laffer took an unorthodox approach to some of the basics of the campaign trail, failing to show at many candidate forums.

Despite the problems - a recent California Poll showed Laffer tied for fourth place with 8 percent of the vote - the economist remains optimistic.

''This is a challenge, in the nice sense of the word,'' he said. ''I don't think I've lost yet.''

In Michigan today, Republican Jacqueline McGregor announced her intention to seek the nomination to again challenge incumbent Democratic U.S. Rep. Howard Wolpe of the 3rd District.

Mrs. McGregor, 47, of Delta Township was defeated by Wolpe in the 1984 race by a 53 percent to 47 percent margin.

''I can beat him this time and I'm pretty optimistic about it,'' said Mrs. McGregor, the only announced candidate for the Aug. 5 GOP primary.

Wolpe, 46, was first elected to represent the district in 1978. The Lansing Democrat is expected to seek re-election for a fifth term.

Mrs. McGregor quit her $57,480-a-year job as Reagan's education adviser last month.