The tomatoes are ripening again in northwest Ohio, destined for the juice, soup and sauce that feeds America, and a small bunch of migrant farmworkers is again planning not to pick them.

Instead, from a run-down building next to the Catholic church in what passes for Toledo's barrio, Baldemar Velasquez and his Chicano compadres are gearing up for another round of a seemingly quixotic battle over the tomato.

They're in their third year of promoting a nationwide boycott of Campbell Soup Co. and Libby, McNeil & Libby products; in their fifth year of refusing to pick tomatoes for farmers who sell to those two companies.

Thwarted by the farmers, the Farm Labor Organizing Committee (FLOC), which Velasquez founded and continues to head, is trying to improve migrants' wages and benefits by pressuring the processors who control prices and contracts.

An Ohio Senate investigation, headed by state Sen. Neal F. Zimmers Jr., held last year that the processors--Campbell, Libby, Heinz, Hunt-Wesson--are directly responsible for workers' welfare by virtue of their dominance. None of the companies would submit testimony to Zimmers' committee.

Despite huge public expenditures and new protective regulations, Zimmers reported that little had changed for the better in the work camps. He wrote that "very basic questions of human rights and serious financial questions that affect all aspects of the tomato industry" were raised by the inquiry.

On this backdrop, the churchmouse-poor FLOC doing battle with a couple of the world's biggest food-processing conglomerates might seem a preposterous notion. But in real life, it is a serious test of wills.

Campbell, while denying the FLOC boycott has had any impact on its $2.5 billion-a-year sales, has met twice with Velasquez recently to talk about the union's demands and "common concerns," as a company spokesman put it. More meetings are anticipated.

"We buy only about 20 percent of Ohio's tomatoes and we buy them nowhere else in the Midwest, unlike other processors," said Roger Duncan at Campbell headquarters in Camden, N.J. "Our position is that Campbell is being singled out as a symbol."

In fact, Campbell is being singled out. After Libby sold a major canning plant at Leipsic, south of here in Putnam County, the firm became a more elusive target.

"We are accentuating Campbell--they are the known leader of the industry," Velasquez said. "We've been sending out people to tell our story and the whole boycott is experiencing a momentum now."

Last week, for example, the Catholic diocese of Columbus joined an Ohio Council of Churches resolution supporting the boycott, which covers Campbell brands as well as Campbell-owned Swanson Foods, Pepperidge Farm, Vlasic pickles and Godiva chocolates.

Several dozen labor union locals, the Indiana and Ohio AFL-CIO, Cesar Chavez' United Farm Workers and a variety of other religious organizations also are supporting the FLOC protest. The FLOC-Campbell talks, Duncan said, were arranged by an arm of the archdiocese of Boston.

FLOC, meanwhile, continues to send out broadsides attacking the company. FLOC raises money by selling buttons, stickers and T-shirts that depict a can of "Cream of Exploitation Soup" on the familiar red and white Campbell label.

The idea, of course, is to pressure the company into serious discussions about better working conditions for the migrants, who either pick tomatoes by hand or work on the harvesting machines that some farmers were required to use under terms of their 1979 contracts with Campbell.

Duncan said Campbell requires its farmer contractors to comply with all state and federal labor laws, but, "it's tough for us to tell a grower to go beyond the law." As for Campbell pressuring the rest of the industry, he said, "We hope the industry will follow suit, but we can't tell them what to do."

Velasquez, 35, who grew up in a Mexican-American migrant family, doesn't buy that approach. He and FLOC think a giant like Campbell has far more influence on farmers and food processors than it admits.

"When we get Campbells to the negotiating table, we think we then can approach the farmers," Velasquez said. "We want the processing industry to put guarantees for workers--and farmers--in their contracts and we want processors to pay certain amounts in those contracts that are earmarked for the workers."

Processors now contract with the farmer at a per-ton rate, while prescribing how the tomato is to be grown, cultivated and harvested. Last year's typical contract paid a farmer $71 a ton for tomatoes--something like 3 cents per pound. A machine-picked acre yields about 15 tons; a hand-picked acre, 25 tons.

FLOC's boycott is the outgrowth of a campaign that began in 1967, when young Velasquez and his farmworker father organized the committee. Out of money, they couldn't get back to their home in south Texas and settled in Ohio.

Velasquez finished high school in Putnam County, then attended several colleges, returning to the fields with his family each summer. "We did sugar beets in Ohio, strawberries and cherries in Michigan, then back to beets and potatoes. Tomatoes were usually for weekends," he said.

"We were really naive when we began. We had problems with minimum wages and with living conditions in the migrant camps. I thought we only had to point out the problems and they would be solved. It dawned on me that the farmers and migrant-aid programs were not going to do what was needed."

FLOC had surprising success in its first organizing effort in 1968. It struck tomato farmers in Lucas County, outside Toledo, and won higher wages. But farmers protested that they could not negotiate when they didn't know how much their cannery contracts would pay.

"That began our education," Velasquez said.

During the next 10 years FLOC worked to build its base (membership is now over 1,100) while negotiating contracts with about 70 individual tomato growers in this area. The problem, in FLOC's eyes, was the processor who dictated terms to the growers. But processors wouldn't talk to FLOC.

The union became more militant in 1978 and decided to pressure the canning firms. FLOC voted to strike in Putnam and Henry counties by refusing to pick tomatoes for farmers who sold to Libby and Campbell. Pickets blocked the Libby plant at Leipsic and the Campbell facility at Napoleon.

The strike continued in 1979 and tempers flared. There was picket-line violence, farm-community reaction against the workers and FLOC's attorney was assaulted and hospitalized by Putnam County sheriff's deputies.

A federal judge, Don Young, issued a restraining order, still in effect, directing Sheriff Robert Beutler to stop harassing FLOC members and to get no closer than 30 feet to an FLOC group unless there was a disturbance.

County newspapers railed at the decision; the Putnam County Sentinel editorialized that "a bloodbath will ensue" if courts continued meddling. The sheriff got an award at a law-and-order day.

Feelings have subsided somewhat, but FLOC continues picketing selected farms. "This is very slow, progress takes time," Velasquez said, "but we intend to stick with it. My satisfaction is to prove these farmworkers can represent themselves."