Tax law may be a damper for professionals who go 'inc.'

''I don't know if I will unincorporate or not,'' says Alan Vogeler, a partner in the New York law firm of Boyle, Vogeler & Haimes. ''I haven't talked to my tax adviser yet.

''But whatever I do it will certainly be in light of these new considerations.''

These are the pension-plan provisions in the new law, Tax Equity and Fiscal Responsibility Act of 1982, passed by Congress Aug. 20. It will be effective for taxable years beginning in 1983.

As Peter Gilman, a pension specialist at Touche Ross & Co., a nationwide accounting firm, notes, ''The main thing to realize is that this bill effectively wipes out the distinction between corporate and noncorporate pension plans.

Mr. Vogeler is one of thousands of professionals nationwide who, for business and nonbusiness reasons, have incorporated themselves. His firm, typical of other ''professional corporations (PCs),'' is defined as ''a partnership which includes professional corporations.''

He and three other partners in the firm incorporated themselves this year primarily for the pension benefits. He now faces a question: If pension benefits are substantially reduced, and if the additional corporate paper work and costs remain, are the other business benefits of incorporation sufficient reason to remain incorporated?

''I incorporated basically for tax and pension-planning purposes - for the tax deferral inherent in corporate planning and the tax-free income,'' Mr. Vogeler says. ''I'm still deciding what I'm going to do. I haven't even read it (the new tax bill) yet, but the fact that the maximum benefit has been reduced and the early retirement age has been raised are clearly important factors.''

He adds, however, that he would not like to lose the ability he has as a corporation to adjust the year in which his income is taxed.

''I'll wait for the CCH (Commerce Clearing House) report on it. It ought to come out within the next month. Hopefully that will clarify things. Then I just have to make a decision, I guess.''

Vogeler's situation is similar to that of many other professional corporations. As for the others, he says that at this point ''some don't know, some haven't read it yet, and some don't want to know.''

Thomas J. Ward, also of Touche Ross, says ''the bill is so new and so sweeping that it virtually limits any one person from being an expert. Anyone who says he is is either a superman or not telling the truth.

''One thing is clear. The bill makes big changes.''

Under it:

* The maximum yearly contribution to a corporate defined-contribution pension plan is reduced from $45,475 to $30,000. The maximum annual benefit under a defined-benefit plan is reduced from $136,425 to $90,000. The maximum contribution to a defined-benefit plan is determined by an actuary who, working backward from the desired benefit figure, comes up with the yearly amount needed to produce that benefit by the time of retirement. The bill is significant because reducing the benefit reduces the amount of tax-free income that can be set aside each year.

* Cost-of-living adjustments for corporate pension plans are frozen until 1986, when they will include Keogh plans.

* The maximum contribution to the Keogh plans (retirement savings plans for self-employed individuals) will increase from $15,000 in 1982 to $20,00 in 1983 to $30,000 in 1985.

* The overall limit on combined pension plans - where both a defined-contribution and defined-benefit plan are included - is reduced from 140 percent to 125 percent of a single plan's dollar limits.

* Plan participants would not be allowed to borrow more than the greater of $ 10,000 or half of the vested benefits, with a $50,000 maximum for loans taken after Aug. 13, 1982. Excess loans will be taxed as early distributions unless repaid within five years, with a longer period for principal residence loans.

* The early retirement age for defined-benefit plans is raised from 55 to 62 years.

Touche Ross notes that 1983-84 is the only year for favorable tax treatment for liquidating these corporations. It also notes that the Internal Revenue Service has added a sleeper to the bill. This allows it to tax at rates for individuals any corporate entity for a personal service organization substantially all of whose services are performed for one other corporation, partnership, or entity and to tax net income directly to the shareholder - a change that may spell the end of these organizations.

Mr. Gilman adds, ''Being incorporated adds complexity to your life, not to mention higher professional fees.

''But one important aspect of the corporate pension plan is substantially unchanged. That is the ability to borrow from the fund. Unincorporated individuals who have Keogh plans can't borrow from them.

''So although other benefits are eliminated, that provision alone may be enough for many PCs to stay incorporated.''