About 3.7 million families and individuals with income at and somewhat over the federal poverty line would be lopped off the income tax rolls by the bill the House Ways and Means Committee passed Thursday to stimulate the economy.

The part of the bill that would free these people from the tax collector is the increase the committee approved in the so-called standard deduction allowed taxpayers who do not itemize.

Given that increase, no family of four with an income of $7,000 or less would owe federal income tax. Under current law this "tax threshhold" for a family of four is $6,100. The government poverty line for a non-farm family of four this year also is expected to be avout $5,109.

The official poverty line is adjusted each year to take inflation into account. The line for this year will not be published until April. Last year it was $5,500 for an urban family of four.

The line is higher for larger families, lower for smaller ones and those living on farms. For single, non-farm individuals last year it was $2,800. The tax threshhold for such individuals under current law is $2,700. Under the committee bill it would rise to $3,400.

The tax threshhold is currently determined by three separate provisions in the law. The first is the personal exemption of $750 that goes to each taxpayer and each dependent. For a family of four that totals $3,000.

The second provision is the $35 credit that goes to each person covered by each tax return. Experts say these $35 credits are equal to $250 deductions. For a family of four the credits are thus worth $1,000.

The last provision is the standard deduction. The minimum standard deduction for a couple thing a joint return is $2,100 under the law. President Carter proposed and the committee agreed to raise this to $3,000.

Thus family of four with a gross income of $7,000 could reduce its taxable income to zero under the committee bill: it would subtract $3,000 in exemptions, take off another $3,000 for the standard deduction and have the fine $1,000 offset by its $35 credits.

A single individual would have on $750 exemption and one $35 credit, equal to a $250 deduction. In addition, under the committee bill the standard deduction for individuals would be $2,400, as against the present minimum of $1,700.

The increase in the standard deduction would be a "permanent" tax cut beginning with 1977 taxes - due in full in April of next year.

The cut would be reflected in reduced withholding rates and increased take-home pay beginning several weeks after passage of the legislation - hopefully by late spring.

For all of 1977, government revenues would decline by about $4 billion. About 55 per cent of this would go to families and individuals with incomes below $10,000, and nearly 90 per cent to those with incomes under $15,000.

In all, about 45 million taxpayers, or close to two-thirds of the total, would have their taxes reduced, but for many the reductions would be very small. Ways and Means statiscians said Thursday that the maximum reduction for any one taxpayer would be a little more than $170 for the year as a whole, or about $3.50 a week.

Taxes of those who itemize deductions - about 30 per cent of all taxpayers - would not be affected by the bill. Itemizes tend to be in the upper income brackets.

Congress has regularly raised the standard deduction in recent years as a way of cutting taxes generally to offset inflation, and a way of moving families and individuals at the lowest income levels off the tax rolls.

The recommended increase in the standard deduction is separate from the $50-per-person debate of 1976 taxes that the President also proposed and the committee approved. These rebate checks would be mailed out in May and June. For a family of four the check would be $200, except that there would be no rebates for those with income exceeding $30,000 a year and reduced amounts for those between $25,000 and $30,000. For example, a family with a $27,500 income would receive a rebate of $25 per person.

In addition, the bill provides that checks of $50 per person be sent to most nonetaxpayers - mainly nontaxpaying Social Security and welfare recipients. Most of these checks would not go out until July and August.

To some extent, however, all of this is speculative. The bill still must go to the House floor early next month, then to the Senate. It is virtually certain to be amended in some respect along the way.