THERE'S A NEW political math to study this fall. The "base number" of this math is 13 - which, when coupled with different factors based on where you live, how much you pay in taxes and who the incumbent is - usually adds up to less than you thought. Still, the tax burden is very much on the minds of voters and the various proposals are bound to attract serious attention.

In Maryland - where no candidate seems to be without a plan - one of the latest proposals comes from J. Glenn Jr., Republican candidate for governor. Mr. Beall would eliminate the state property tax, now at a rate of 20 cents for each $100 of assessement. He also would raise the personal income-tax exemption from $800 to $850 and then gradually to $1,000 ata rate of increase equal to inflation. So if you could know how much your future assessments will be, you could figure out how much you might save, even if it isn't related at all to your ability to pay.

All of this is related, however, to the state's ability to pay - and so the Beall math includes a formula limiting annual increases in the state budgets to no more than the rate of inflation, for which there are no firm numbers, either. Mr. Beall also has proposed offsetting revenue reductions by freezing government hiring. A hiring freeze is what Acting Gov. Blair Lee III dramatically imposed last June when he was an active candidate - and what he has quietly modified now that he's not running anymore.

Mr. Beall's Democratic opponent, Harry R. Hughes, is working on a possible further graduation of the income tax and a lowering of all property taxes - state, county and city - by restricting the uses of such funds. Only police and fire protection, trash collection and road construction would be paid for by the property tax.

There is also local math to factor in. In Montgomery County, a group called TRIM (Tax Relief in Montgomery) has a proposal on the ballot that would put a ceiling of $2.25 for each $100 of property assessment - though experts aren't sure whether it would apply to the "real property tax" rate of $2.60 or the typical overall property tax rate of $3.60, which includes extra taxes for services such as recreation and fire protection.In Prince George's, there is TRIM (Tax Relief Initiative for Marylanders), which would freeze property tax revenues at the 1979 level. And candidates in both counties have still other proposals and plans.

Tax relief is an attractive objective, of course, and no candidate can afford to ignore the subject. But in assessing the various campaign proposals, voters will probably discover that no combination is likely to produce smaller total tax bills for them the next time around. At best, some of the plans will slow down the rate at which those bills go up.