If last week's foul weather hadn't wiped out President Reagan's tour of Baltimore's fledgling "enterprise zone," he would have met Fred Barrett. It might have been good for both of them.

The Jamaica-born, U.S.-educated Barrett is a virtual computer printout of Reagan's notion of the American spirit. He is the creator of what is simply the best stereo tuner in the world. (Modern Hi Fi and Music magazine has called it "the finest performing tuner ever"; Japan's leading hi-fi magazine awarded it its coveted "State of the Art" Award.)

Reagan would have been delighted to see this incredible machine being manufactured in what five months ago was an abandoned warehouse in Baltimore's Druid Hill section by young blacks who were, until Barrett put them to work, unskilled and unemployed. He would have beamed when Barrett told him, as he had planned, that he was committing himself to "build an urban enterprise model for you."

What Reagan wouldn't have learned, on his short tour, is that Barrett is clinging to his business by his fingernails. The story behind his troubles is almost as incredible as his Sequerra I tuner.

He was doing close to $4 million in sales in 1973 when his success brought him to the attention of President Nixon, who appointed him the first executive director of the Consumer Product Safety Commission. Barrett declined the GS-18 salary that went with the job and became a dollar-a-year man.

Then his dream started to crumble. Because his Washington job removed him from the day-to-day management of his business, then based in New York, the Small Business Administration ruled that he was no longer eligible for the SBA's 8(a) set-aside program for government contracts. (A major source of his income had been the electronics equipment he was making for the military.) Without those contracts, Barrett knew there was no way he could meet the payments on his $350,000 SBA loan, so he quit the government to return to his business.

Too late. By that time he had already been forced to lay off 129 workers. He lost $500,000 he had scrounged from family and friends and, on top of that, was hit with a lawsuit for the now-defaulted SBA loan.

Since then his life has been a constant, mostly losing, battle against the government. He did come close to victory a couple of times. The Ford administration had promised to bail him out, but then Ford lost the 1976 election to Jimmy Carter. Carter's people were ready to put him back in business, and then Carter lost his re-election bid. The Economic Development Administration, which had worked out a package that included refinancing of the $350,000 indebtedness and a new batch of federal contracts, dropped the whole thing when the default was referred to the Justice Department.

In recent months, he has been trying, without much success, to get the Reagan people interested in his situation. Just yesterday, he learned that he will have to appear in the U.S. District Court in Brooklyn on Feb. 5 to fight off a default judgment.

Ironies abound. He first got into financial difficulty because he tried to serve his government. His only chance of getting out of financial difficulty--and of repaying the SBA loan--is for the government to renegotiate the loan and recertify him for government contracts. The government is in the absurd position of demanding its money while making it impossible for Barrett to produce it.

Electronics manufacture is one of the more labor-intensive enterprises in America, one for which the training period is short and which demands no expensive outlays for plant. (Barrett hasn't even taken the boards off the old Baltimore warehouse where he is now trying to launch his comeback, and after only 41/2 months his 12 employees are earning between $4 and $5 an hour.)

"The great thing," he said over a recent lunch, is that we've already got a lead product with an international reputation. We could easily flow 50 other products behind that, hiring and training new people as needed, if we could get the government to work with us. I don't mean to sound immodest, but we could build the city of Baltimore."

Unfortunately, Barrett's extraordinary mind, which ought to be devoting itself to more of his electronic marvels, is occupied these days with something much more mundane: simple survival.