The Senate approved legislation last night that places a new permanent lid on mortgage interest rates in the District of Columbia and assures an end to the two-week freeze on home mortgage lending in the city.

The measure now goes to the White House, where a spokesman said President Carter is expected to "act quickly" and sign the bill.

The new 15 percent mortgage interest rate ceiling may be law by Monday morning, and all 66 mortgage banking firms in the city and about 12 of the District's 16 savings and loan associations are expected to resume making home loans immediately, according to mortgage banking and savings and loan industry officials.

But lending officials said prospective home buyers can expect to pay record-high interest -- 14 percent or more in some cases -- and may be required to produce down payments of 25 percent or more of their new home's purchase price.

In addition, the officials, said, many of the estimated 1,000 prospective home buyers here who had their loan settlements delayed by the funding freeze may now face bigger than expected monthly mortgage payments because of interest rates that have climbed since their sale.

Interest rates have climbed another 1/4 to 1/2 percent in the two weeks the mortgage lending freeze was in effect, depending on the lender. That means a homeowner with a 30-year, $70,000 mortgage would pay $802.20 a month in principal and interest at 13 1/2 percent, compared to $774.90 with a 13 percent rate.

The mortgage lending freeze was prompted by D.C. Superior Court Judge George H. Revercomb's decision last month that invalidated the city's moratorium on condominium conversions because the City Council had twice used emergency legislation to extend the ban.

Although Revercomb's ruling did not deal with mortgage interest rates, the Federal National Mortgage Association (Fannie Mae) and the Federal Home Loan Mortgage Corp (Freddie Mac) cut off their purchases of mortgages in the city on grounds that the council's latest approval of mortgage interest rate legislation, passed with emergency powers Oct. 5, might be similarly illegal.

Together Fannie Mae and Freddie Mac provide about 11 percent of the home loan money in the city -- $84.4 million in the first nine months this year, the single biggest source here of mortgage money.

Individual borrowers receive their loans from savings and loan associations and mortgage banking firms, which then often sell them to secondary investors, including Fannie Mae and Freddie Mac. The money the local lenders get in return is then used to make more loans to home buyers.

With the cutoff in Fannie Mae and Freddie Mac funding, numerous lenders in the city stopped making new loans or taking new loan applications and delayed loan settlements. The cut-off came at a time when the housing industry here was already beset by the high mortgage rates and a scarcity of mortgage money.

Both Fannie Mae and Freddie Mac said yesterday they would resume purchases of loans on D.C. homes as soon as Carter signs the legislation.

After the funding cutoff was announced by Fannie Mae, the City Council moved quickly to approve permanent legislation setting the 15 percent mortgage rate ceiling.

But that legislation faced one more hurdle before it could take effect. Under the city's limited home rule authority, Congress retains the right to review nonemergency city-passed bills for 30 legislative days. Because days on weekends and during congressional recesses are not counted, the process sometimes takes several months.

The legislation approved by the Senate on a voice vote yesterday, and by the House on Tuesday, waived that review, on a one-time basis only. So the mortgage interest rate bill could take effect immediately.