These days, when Cabot Corp. in Waltham, Mass., writes checks for charitable contributions, the company's 3,000 domestic employes have a lot to say about where the money goes and how it will be spent.

"We want to recognize employes who go beyond their jobs and become social entrepreneurs in their communities," said Ruth Scheer, vice president and executive director of the Cabot Corp. Foundation.

Some 60 percent of the half million dollars the company spent on cooperative projects this year was targeted by employe teams.

Projects as diverse as building a playground to operating a van service to transport elderly and low-income residents for medical care got the company stamp of approval.

Cabot, in some respects, is typical of the route many American corporations are taking in managing their charitable contributions: Many of the biggest corporate givers are becoming more tightfisted, but are more heavily involved in how their dollars are spent, with one of the major areas of focus being education.

Among the 292 major corporate donors that the Conference Board tracked in 1985 and 1986, charitable contributions rose a modest 3 percent, continuing evidence that increases in corporate dollars going to charity have been sharply curtailed in the last two years.

"Economics has a great deal to do with it," said Linda Cardillo Platzer, senior research associate at the Conference Board. "Contributions are closely related to corporate income."

At one point, there was a push to encourage companies to dedicate 2 percent to 5 percent of their pretax income to charity.

Overall, U.S. companies last year gave nearly 2 percent of pretax income, about the same as the previous year.

The nation's top 75 givers, however, gave more than 2 percent of pretax income to charity, according to the Conference Board.

Among a larger universe of 372 major service and industrial companies the Conference Board surveyed for their contributions for 1986, amounts given actually declined almost 2 percent, to $1.7 billion, or 37 percent of all charitable giving by U.S. corporations.

Total contributions by all American companies, estimated by the Council for Aid to Education, were $4.5 billion last year, up 2 percent from 1985.

Part of the slackening in the increase in contributions is attributable, Platzer said, to the economizing that some oil companies have done on the charitable front as their own balance sheets have suffered from the downturn in oil prices.

Leveraged buyouts, mergers and acquisitions and the streamlining of corporations also have taken their toll.

"The new guy comes in and just doesn't have the same priorities as the old," Platzer said. "Things that used to be automatically increased are reevaluated on a case-by-case basis."

The pattern of slower growth in giving, which began in 1985 and stands in strong contrast to the 13 percent to 26 percent annual gains posted in the last decade, would have been even more pronounced if companies had not turned to products, land and equipment to supplement their contributions.

The Conference Board reported that among the 25 largest corporate donors last year, noncash contributions represented more than 30 percent of their total giving.

The tax law allows companies to deducsecurities and other assets up to their fair market value, and there are even more generous deductions for products given for use in scientific research and training in the biological and physical sciences.

Although there was an increase in money given to culture and the arts, the biggest chunk of corporate contributions from the 372 major companies surveyed by the Conference Board was for education in 1986.

Of the $1.7 billion given, some 43 percent went to fund education-oriented projects and programs, up from 38.3 percent in 1985. Among the smaller sample of companies watched in both 1985 and 1986, education as a portion of overall giving shot up a dramatic 17 percent, said Jane Hammond, director of research for the Council for Aid to Education.

"More and more, there has been a difference in the quality and motivation of corporate contributions and contributions to education," said Paul R. Miller, vice president of the Council for Aid to Education.

"The education stuff has an investment quality about it," he said.

BellSouth Corp. is trying to improve the quality of education in the nine southern states it serves.

"There must be a solid commitment ... to fund basic quality in the public education system," John L. Clendenin, chairman of BellSouth, said in a recent speech.

"This commitment was missing in the southeast for many years and we're working hard to make it up," he said.

The company set up the BellSouth Foundation last year with an endowment of $25 million.

So far, it has handed out $1.6 million to fund six programs that range from assessing the quality of math instruction given to middle school students to expanding the recruiting and improving the education of minority teachers.

"By focusing on education, we think we can improve the quality of life in the region, strengthen the employe force and foster greater economic development," said Thomas Crawford, a BellSouth spokesman.

Although about 75 percent of the corporate dollars given to education go to colleges and universities, companies are paying more attention to what happens before students reach that level.

Some are entering into partnerships with public schools, volunteering their employes' time as tutors.

Others are pouring money into upgrading specific subject areas in school systems.

The Washington Post Co. hopes to motivate academic achievement at the undergraduate level with a scholarship program it started for the 2,300 students at Eastern High School in the District.

Those students who earn at least a B grade each semester get $500 set aside for them in a special "account," which then can be used at any college or accredited trade school.

Most area colleges have promised matching funds.

"I think we are at the beginning of a trend," the education council's Hammond said.

"More money is being allocated to the kindergarten- to 12th-grade levels. Expenditures are in the planning stages and money has been committed," he said.