A key Ways and Means subcommittee yesterday approved legislation guaranteeing a tax exemption for a wide range of employe fringe benefits ranging from parking to tuition--providing that they are made available to everyone from the janitor to the corporate president.

The subcommittee action, taken behind closed doors, represents a major concession to such groups as airlines, universities and retail stores, many of which offer employe discounts on services and goods as a way to provide compensation that is tax-free to the employes.

Under existing law, many fringe benefits would be considered taxable income, but Congress has kept the matter in limbo since 1978, when it barred the Internal Revenue Service from regulating them.

In addition, the proposal, if enacted, would represent a major setback for reform proponents of broadening the tax base because it would exclude an increasingly common form of payment to workers.

Although the proposed bill would appear to meet the objections of most of the special interests involved in the long struggle over the issue of taxing fringe benefits, the nondiscrimination section is likely to prove highly controversial.

It requires companies to hand out the fringe benefits to all employes, or to make the benefit available on some neutral basis, such as length of employment, rather than giving them out as special benefits to executives.

Similarly, universities, many of which now limit tuition waivers to the children of the faculty and administration, would be required to make the benefit available to the children of all employes, including secretaries, librarians, kitchen employes and maintenence workers.

Another form of fringe benefit handed out by many corporations exclusively on the basis of rank is free or discounted parking. Under the proposed law, for that to continue to be a tax-free form of compensation it would have to be available to all employes, or distributed on the basis of seniority or need--for the salesmen who need their cars for work, for example.

A company could continue to hand out a fringe benefit on a discriminatory basis, but the recipient would then be required to pay taxes on the benefit. If, for example, a television distributor gave 30 percent discounts only to management-level employes, those employes who took advantage of the break would have to pay taxes on the 30 percent reduction in the cost of the television set.

The legislation limits employe discounts on retail sales to the cost of the goods to the company. If, then, a hardware store bought electric saws at $100 and sold them for $200, it could give employes a discount of up to $100 off the retail price, but it could not reduce the price to the employes below the $100 wholesale price the store paid.

In the case of services, the discount would be limited to 20 percent. A dentist, for example, who normally charged $80 for a complete examination and cleaning of teeth could reduce the fee for his receptionist by only $16, to $66.

The measure would also limit fringe benefits to what are called "lines of business." The effect of this restriction is to prevent conglomerates from providing all employes discounts from all subsidiaries. A firm owning a chain of clothing stores and a separate subsidiary producing personal computers could only give a discount on clothes to the employes of the clothing stores and a discount on computers to the employes of the computer subsidiary.

This restriction would not, however, prohibit an employe of, for example, TWA from getting a free standby seat on an Eastern Airlines flight, or the child of an employe of Georgetown University from getting free tuition at the University of Pensylvania.