When Congress considers tax legislation, there's often a fine line between the sublime and the ridiculous. While much of the tax legislation the lawmakers propose is serious and well-drafted, other bills are so patently fanciful they end up as the butt for congressional one-liners.

With this being an election year, the supply of silly tax legislation is all the more bountiful. Here, for those who think tax law has to be dull, is a compendium of some of these measures - with a few non-congressional embellishments designed to highlight some of the foibles:

Item: Sponsors of two rival bills to provide tuition tax credits have joined forces behind a massive $4.5 billion proposal that combines tax breaks for college students and elementary-and-secondary school pupils. The coalition is designed to broaden the measure's support.

If the two sides still don't have enough votes, maybe they could consider merging with sponsors of the popular home-insulation tax credit proposal how pending in the Senate. The result would be a new all-purpose College Tuition and Storm Window Tax Credit that supporters contend would be all but unstoppable. The measure would offer a tax break for everyone who ever wanted to avoid a draft.

Item: Sen. Mike Gravel (D-Alaska) has a proposal to lower taxes for Alaska and Hawaii residents by increasing their personal exemption to $850. Reason: Their higher living costs require higher pay - and make their taxes higher, to boot.

What's needed now for equity is a companion bill that would boost the tax burden for residents of Mississippi and Arkansas, whose living costs - and taxes - are proportionally lower. With a little more effort, Congress could set different federal income-tax rates for each of the 50 states, and revise them each session.It could keep Congress out of trouble for most of the year.

Item: Rep. Alvin Baldus (D-Wis.) is sponsoring a bill that would allow individuals to clain an investment tax credit for farm and ranch equipment that they purchased "from an ancestor."

Just watch the Internal Revenue Service ruin it by requiring a freshly signed receipt.

Item: Sen. Russell B. Long (D-La.) is seriously pushing a plan to give taxpayers the first $100 of President Carter's proposed energy tax rebates in the form of a voucher that can be used only to buy stock in oil companies. The Finance Comittee would help the oil firms attract more needed investment to step up exploration and production.

Can you imagine a similar scheme for cutting back cigarette consumption? First tax cigarettes severely, then rebate the money for consumers who buy stock in Phillip Morris.

Item: Rep. Robert F. Drinan (D-Mass.) is sponsoring a bill that would deny all companies any tax deductions for so-called "institutional" advertising that is not related to the sale of their products or services.

One wag suggested recently that, Drinan may have proposed the billin anger after he learned that Lord Bellamy - the left-of-center father on public television's "Upstairs, Downstairs" - actually was a Tory.

Item: Rep. John F. Seiberling (D-Ohio) has introduced abill that would provide for a tax deduction for gifts and donations to the United Nations.

How about a similar tax break for contributions to the North Atlantic Treaty Organization and the International Monetary Fund. ("This landmine was donated by . . .")

Item: Sen. Frank Church (D-Idaho) is considering a spate of new tax breaks for the elderly - despite Treasury and OMB figures that show older persons already receive one-third of federal benefits and tax breaks.

Why not higher taxes on kids, just to balance things out? Figures show millions of children actually escape payment of taxes each year. And authorities are doing nothing about it.

Item: Rep. George E. Brown Jr. (D-Calif.) has introduced legislation that would bar the usual business deductions for costs in advertising alcoholic beverages.

He's trying to crack down on the three-martini ad.

Item: Rep. John M. Ashbrook (R-Ohio) is sponsoring a measure that would allow parents a deduction for the money they spend on their cars in driving their kids to school.

What about a companion lunchbox-and-schoolbag tax credit to go along with Ashbrook's proposal? There'd probably be some controversy over whether the benefits should go to youngsters in parochial schools. But a quick court test would resolve that.

One perennial that seems not to have sprouted this year is the proposal by Rep. James A. Burke (D-Mass.) for a tax writeoff for the cost of home garden tools and seeds. No doubt there'll be some disappointment. A lot of people whose tomatoes turned out bad in 1977 had been hoping to claim them as a loss.