People who have an individual retirement account and a 401(k) tax-deferred retirement plan face a dilemma: whether to make IRA contributions now and risk penalties later, or wait to invest and forgo maximum interest and dividends.

In December, the House, as part of tax reform, approved changes in retirement accounts to cut back the amount of tax-deferred income individuals can squirrel away. Under the bill's terms, the changes would be retroactive to Jan. 1, 1986, no matter when the measure becomes law.

Current law permits an employe to contribute up to $30,000, or 25 percent of compensation annually, to a 401(k) plan run by his or her employe. The employe also can contribute $2,000 annually to an IRA.

The House would impose a $25,000 cap on the 401(k), with the employe's annual contribution limited to $7,000.

And it also would effectively prohibit the $2,000 IRA contribution for many people with a 401(k) plan, and sharply limit it for others.

It did this by inserting in its bill a provision that would reduce an individual's IRA deduction by one dollar for each dollar put in a 401(k) plan, the contribution to an IRA would be limited to $500.

The house bill thus would affect anyone who puts in more than a total of $2,000 in IRA deductions. Dallas Salisbury of the Employee Benefit Research Institute estimates that perhaps 500,000 persons in the $50,000 plus bracket would feel the full impact.

Contributions toward an IRA for 1985, which can be made before April 15, would not be affected.

IRAs still are allowed under the proposed legislation. But if a person opted to put $2,000 into one, nothing could go into a 401(k). And for many people eligible for a 401(k), this would not make economic sense.

First, the amount that could be excluded for taxation under the House bill in a 401(k) is much larger than under an IRA -- $7,000 versus $2,000.

Second, many employers choose to match their workers' contributions wholly or in part, something that is not available for IRA holders.

Of course, the House version of the tax reform bill may never become law, or if it is enacted, the effective date may be changed. The history of tax legislation points that way. But no one can be sure. And if a person were to go ahead and, say, buy bank certificates of deposit for an IRA and then the bill became law, he or she would presumably have to give up the 401(k) or pull the money out and face penalties.

Although there is no current data on 401(k) and IRA participation, Salisbury estimates that if everybody who now has both plans abandoned his or her IRA to stick with the 401(k), contributions to IRAs would drop by as much as $3.6 billion, or 10 percent of 1985 sales. (A similar provision affecting 403(b) tax-sheltered annuities for employes of nonprofit organizations could boost that figure by perhaps half again.)

Besides individuals, who will be unable to set aside as much tax-deferred income for their retirements, the biggest losers under the House bill stand to be banks and savings institutions, which have 57 percent of the $200 billion-plus IRA market, according to The IRA Reporter in Cleveland. Mutual funds and brokerages, by contrast, are likely to handle both types of funds, and therefore suffer less damage, according to Salisbury.

But David Silver, president of the Investment company Institute, representing mutual funds, predicts IRA contributions could drop as much as $8 billion, or 20 percent of 1984 sales amounting to $36.4 billion, as some 4 million people with 401(k) and 403(b) plans abandon IRAs.

According to a member of the House Ways and Means Committee staff, who asked not to be named, the House aimed not only at curbing excesses but also at preventing discrimination. Rich and poor workers alike can contribute a maximum of $2,000 each to an IRA, but the tax deduction is worth more to the rich one. The 401(k) plan has built-in safeguards to assure that the lowest paid employes in a firm get as good a deal as the highest paid.

Such a situation usually arises in small firms where there is a large difference between compensation for top people and other employes. To comply with a complex formula designed to prevent the top people from according large benefits to themselves at the expense of others, firms at times may have to make contributions for non-participants. For example, a lawyer earning $140,000 annually could contribute $7,000 or 5 percent of compensation. If the firm matches that, it has to kick in approximately the same percent of salary for the secretary, whether the secretary contributes or not. So, the firm would put $800 in the retirement fund for the secretary earning $20,000, even if he or she puts in nothing.

There have been reports as well that the integration of the two retirement plans also was intended to prevent abuses whereby people would fund a 401(k) plan, borrow money from it without penalty to fund an IRA, and take a tax deduction for both.

Banks, savings and loans, credit unions, mutual funds and some brokerages offering individual retirement accounts plan to oppose this provision when tax reform comes before the Senate Finance Committee this spring because it would cut into their sales. Although they would like to retain the status quo, they probably would settle for allowing individuals to fund either an IRA or 401(k) up to a combined total.

Meanwhile, persons who fund both plans now risk penalties. The Internal Revenue Service declined to speculate on the consequences of proposed legislation. But under the current rules for overfunding, it would exact no penalty if excess 1986 IRA contributions are withdrawn before April 15, 1987. If not, a 6 percent annual excise tax would be levied on principal and interest for as long as the money remains in the account. And in addition, the normal 10 percent penalty (which the House bill for early withdrawal-before age 50 1/2 -- would apply.

Since most financial institutions in this area offer IRA accounts with maturities of a year or more, a person who now opens an IRA with such a maturity and has to withdraw the money before April 15, 1987, probably would be subject to a premature withdrawal penalty, ranging from three months to even a year's loss of interest on existing certificates.