The House Ways and Means Committee, trying to overhaul the tax code, is making changes that could reduce the retirement income and alter the financial planning of millions of Americans.

One of the most sweeping actions taken Wednesday, for example, would effectively prevent taxpayers from contributing to an individual retirement account if they have more than $2,000 in a tax-deferred "401 (k)" savings plan.

That change alone could affect the finances of many of the 17 million Americans who contribute to IRAs and the perhaps 12 million to 15 million people enrolled in 401 (k) plans -- tax-deferred arrangements named after their section of the tax code and offered by employers. (Some people participate in both types of arrangements.)

The panel's actions on retirement, like all the other tax changes it has made, have many more hurdles before they can be enacted into law. But their impact would be far broader, at least to the average American, than many of the committee's previous votes in such areas as farming, banking, tax-exempt bonds and accounting.

According to figures compiled by the ERISA Industry Committee, some 56 million people -- 50 percent of all taxpayers -- are covered by some kind of pension plan, including the 401 (k)s. That figure does not include IRA-holders.

The committee voted Wednesday to reduce the amount of money a taxpayer can contribute to a 401 (k) plan to $7,000 and to limit what an employer can put into the plan on an employe's behalf to $18,000. Under current law, employes and employers together can contribute $30,000 or an amount equal to 25 percent of the worker's salary, whichever is less.

Under the committee plan, someone who puts $2,000 or more into a 401 (k) account could not also deduct contributions to an IRA. Someone who puts $500 into a 401 (k), by the same token, would still be permitted to contribute $1,500 to an IRA.

Ways and Means decided to continue to let taxpayers withdraw money from their 401 (k) plans in case of hardship -- a definition that has been stretched to include such purposes as children's college educations -- but would impose a stiff penalty of 15 percent of the amount withdrawn. Under existing laws, a taxpayer making a "hardship" withdrawal must pay taxes on the withdrawn amount but faces no penalty.

Rep. Byron L. Dorgan (D-N.D.), who served on a six-member committee task force that forged the pension proposals, said the changes would affect only the highest-income taxpayers. More than 95 percent of contributors to 401 (k) plans put in less than $6,000 per year, he said.

"We have to find a reasonable limit because the fact is that these incentives cost lost tax revenue," Dorgan said. "We are trying to strike a balance between continuing reasonable incentives and being able to bear the cost of those incentives."

The pension changes enacted by the committee would raise $18 billion in revenue over five years, which the committee hopes to use to offset the cost of lower tax rates.

Other changes by the committee would affect employer-sponsored retirement plans by permitting companies to contribute enough to the plans now to fund a top pension benefit of $77,000 per year, rather than the current $90,000 per year. The $77,000 would be indexed for inflation, but that indexation would not begin until 1988. With a lower ceiling, more workers would bump into the limit. As a result, a greater proportion of employer contributions into the plan -- which are tax-deductible -- would be subject to limitation.

That gap led representatives of employe-benefit groups to worry that companies will have to pick up a greater proportion of pensions out of their own coffers in the future.