The interest rate on FHA- and VA-insured home mortgages will be raised to 12 1/2 percent Monday, a half-percentage-point increase, the federal government announced yesterday. Some housing industry leaders described the move as too little, too late.

The increase, second in a month, comes after a week of growing pressure for a rate hike from lenders and industry analysts who said home sales were being choked off by the growing gap between interest rates in the mortgage markets and the rates set by the Department of Housing and Urban Development. But the Monday rise means that five or six discount points, a level that will continue to force many buyers out of the market, will still be charged, predicted a lender.

In announcing the decision, HUD Secretary Samuel R. Pierce said "there has been a definite upward trend in mortgage rates with conventional loans now generally at 14 percent." The Monday increase will "bring FHA rates in line with current market conditions."

A spokesman for the nation's mortgage bankers disputed Pierce's view, saying that rates in the mortgage markets have gone up a full percentage point in the last month and that the "correct decision" for HUD to make was a rise to 13 percent on FHA loans. The spokesman, Mark Riedy, executive vice president of the Mortgage Bankers Association, called the half-point rise "a political decision" and "a short-sighted mismanagement of policy."

The Reagan administration said Thursday that the White House does not want to see interest rates rise.

From 8 to 10 discount points were being charged with FHA- and VA-insured loans late this week, stalling negotiations on many home sales and barring thousands of would-be buyers from the market, say industry leaders. Each discount point represents 1 percent of the loan amount and points are charged to make FHA and VA loans attractive to investors who buy them in the so-called secondary-mortgage market.

Spokesmen for real estate brokers' and builders' associations deplored the rate increase as a serious threat to the housing recovery that started last year but has been on shaky ground in recent weeks.

Other rate changes to go into effect Monday are a half-point rise in multifamily mortgage insurance to 13 percent, a 1 percent rise in Title 1 mobile home loans to 15 percent, and a 1 percent increase for combination mobile home and lot loans to 14.5 percent.