Spain devalued the peseta today as the government also announced a series of tax reform proposals designed to perk up the sagging Spanish economy.

Government spokesman Ignacio Camunas would not be specific about the new rate for the Spanish currency, but said it would be "realistic." Some financial experts had predicted a devaluation to 20 to 30 per cent.

Earlier in the day, the government suspended foreign exchange dealings as the cabinet met to discuss ways to bolster the economy and halt the run on the peseta.

The government did not say when the foreign exchange markets would be reopened. It was not expected to set the actual exchange rate until the trading floors are opened again.

While the government suspended foreign exchange trading, private banks continue to exchange dollars at the old rate of 69.99 pesetas to the dollar.

Camunas said the the cabinet decided to announce the devalutation at a late-night news conference because any further delay in taking the action - which will make imports cost more and lower the price of goods Spain sends abroad - would have hurt Spanish citizens more.

Banking sources had speculated earlier in the day that the government might not change the price of the peseta until fall and would leave the foreign exchange markets closed indefinitely.

While private banks apparenly continued to do some limited trading in pesetas, most tourists streaming into Spain on vacation found they could not buy local currency. Exchange counters at the French border rolled down their shutters.

Had the government delayed devaluing the peseta they would have been able to collect bigger earnings from the tourists, but apparently the government decided that the run on the peseta in foreign exchange markets and the burdens that imposed on exports were too great to delay devaluation beyong the summer.

Speculation that the Spanish government might devalue the peseta contributed to yet another drop in the U.S dollar's value on European money markets today, dealers said. Gold also was down. Also a factor was the U.S. government's projection of a huge trade deficit for fiscal 1977.