Interest yields at this week's Federal National Mortgage Association regular auction of commitments to buy future home mortgages soared to the highest level in two and a half years, the company reported yesterday.

In another development, FNMA issued its first detailed reponse to proposed new regulation of the firm by the Department of Housing and Urban Development.

Chairman Oakley Hunter said the government agency's proposals of two weeks ago would "drastically change" the way the company operates and result in a takeover of FNMA by HUD that could seriously disrupt mortgage markets.

This week's increase in mortgage commitment yields at was the seventh consecutive rise. It affected mortgages guaranteed by the Veterans Administration and Federal Housing Administration and conventional mortgages not backed by any government agency.

Fannie Mae, as the company is known, said the average yield for government - backed mortgage commitments was 9.362 percent, up from 9.351 percent two weeks earlier and the highest since 9.806 percent, also on Oct. 20, 1975.

FNMA said it issued $218.5 million of commitments for FHA-VA backed mortgages, promising to buy them in four months if offered. The company received 440 bids for $358.8 million and accepted 331 with wields ranging from 9.332 percent to 9.446 percent. In the conventional mortgage auction, FNMA issued $266.4 million of commitments for 356 bids, with yields ranging from 9.552 percent to 9.690 percent, out of 522 bids submitted totaling $444.8 million.

Home mortgage yields have been increasing since January along with interest rates generally, Mortgage bankers, who sell some of their mortgages to Fannie Mae, seek commitments for future purchase at the regular auctions. If interest rates continue to rise, FNMA can be expected to buy a large portion of the mortgages for which it has issued commitments; if rates begin to decline, FNMA would be offered a smaller number.

The Federal Home Loan Bank Board estimated that the U.S. average mortgage interest rate for new homes was 9.15 percent in January, but housing economists say the rate for prime mortgages in the Northeast and Midwest is now 9 1/2 percent.

Some money experts say HUD's recent attacks on FNMA's management have added to a "nervousness" that has helped boost interest rates. HUD has proposed new regulations designed to make FNMA more responsive to "public responsibilities," including increased attention to urban properties.

In his statement yesterday, Hunter said Congress "clearly intended for policy control of FNMA to be vested in its board of directors," when the company was transformed from a government agency to private firm in 1968.

As an example of "regulatory excess" now proposed by HUD, Hunter cited the proposed allocation of mortgage commitments for homes in central cities. Such regulations would "constitute a form of redlining, discriminating against large numbers of home buyers and the home building and home financing industry serving them," he asserted.

Such regulations would force FNMA to halt its auction system and require mortgage leaders to sell to the FNMA loans for which commitments have been issued - rather than being free to shop around for better prices, as under the current plna, according to the FNMA chief executive.

He forecast that HUD's regulations, if adopted, would increase FNMA's borrowing costs as well as home mortgage interest rates.