With only five stealing days left until Christmas, light-fingered thieves are busy with their last-minute "shopping" in dozens of Uncle Sam's outlets here. Favorite items this season are calculators and computers, radios and, of course, the old standbys: wallets, purses and cash.

Despite security crackdowns at many federal buildings, nervy, well-dressed crooks continue to find some government offices easy pickings. And the price -- unless they get caught -- is better than any discount store in town.

The real crime season in government begins around Thanksgiving and continues through January as crooks pick up goods and cash for Christmas, and take advantage of the early darkness to slug people outside the office and make their escapes. Federal officials say that in-house violent crimes appear to be down slightly from last year. But they note that the few remaining days until Christmas, when people carry various extra loads, are a time to be extra careful.

Workers at the Forrestal Building say that two women were mugged at gunpoint recently, and there was a reported rape there in October. Seventy dollars was stolen from an eighth-floor office the other day. Last Friday a brand-new winter coat left the building on the back of someone other than the woman who owned it.

Thefts of government and personnel currency jumped in November when $3,589.41 in government petty funds disappeared and 41 workers reported they had been relieved of $5,224 from their desks. A year ago "only" $1,211 in official cash was stolen in November. Money from individual office thefts was $2,520. December's count isn't in.

Last month thieves stole at least 14 personal calculators from government offices downtown, valued at $415.

People who leave purses, wallets or just cash lying around the office continue to be easy targets. In November there were 67 reported thefts valued at $1,820.75. That is double the number for November 1979, but the cash haul then was still a hefty $1,470.

If last year's experience means anything, the worst is yet to come. In December 1979 federal protective officials got reports of one strong-arm robbery in an agency that netted the thief $292; four aggravated assaults, one against a government guard; 26 government-owned calculators (value $3,684) disappeared; 50 electric typewriters ($37,836) stolen; $470 in government currency removed from offices and $3,684 in personal cash and or government payroll checks stolen.

Security types advise employes to take purses and wallets with them even if they leave the office for a short time; to bolt down or chain typewriters, radios and the like and to be especially careful on payday and the day after when people roaming corridors are busiest.