If you like the idea of lower insurance premiums, are a retiree wondering about a refund from your health plan or one of the federal employes working a four-day week, yesterday was a good day for you in Congress.

This is what happened:

*The House approved a bill sponsored by Rep. Gary Ackerman (D-N.Y.) giving a 30-day extension to the six-year experimental flexitime program that is scheduled to expire Tuesday.

The extension would give the Senate and House time to agree on a bill to make flexitime a permanent program.

About 20 percent of Washington's 350,000-member federal work force is involved in flexitime.

It allows employes to come to work before or after regular starting times, provided they put in an eight-hour day.

Flexitime also exempts the government from the law requiring that overtime be paid after eight hours. That has permitted many workers to put in 10-hour days four days a week.

Unless flexitime is extended those four-day arrangements will end next week.

The House already has sent the Senate a bill to make flexitime permanent.

But Sen. Orrin Hatch (R-Utah) wants it amended to take care of a whole other matter not having to do with flexitime.

He wants to allow private-sector employers to pay below-minimum wages to some teen-age workers.

Labor unions object to that amendment, so the Senate hasn't acted on a permanent flexitime bill.

Senate GOP leaders indicate that they will go along with the temporary extension on flexitime.

*The House Post Office-Civil Service Committee yesterday unanimously approved a bill sponsored by Reps. Mary Rose Oakar (D-Ohio) and Frank Wolf (R-Va.) that would make major changes in the federal health program.

One provision of the bill, which is expected to clear the full House early next week, would remove any ceiling on federal agency payments to employes' health premiums.

The Postal Service now pays up to 75 percent of employe-retiree premiums, while other agencies pick up about 61 percent of their employes' tab.

The House bill would make it possible for the government to pay all of the premiums next year for employes and retirees who chose low-cost plans.

Oakar's bill also would amend the federal health insurance law so retirees can get the same premium rebates already promised workers by 11 plans.

Those premium refunds, which range from $18 to more than $400, have been approved for workers, but the law must be changed so retirees can get them as well.

The Reagan administration supports the rebates for employes and retirees, so the bill shouldn't have any trouble in the Senate.