Boston — With few exceptions, Americans may be best off for the next several days if their approach to the weather is: grin and bear it.
The record-setting low temperatures that spared only the southernmost sections of Florida among the continental United States Jan. 11 and 12 aren't likely to moderate much through the end of the week, say weather experts.
''I don't see anything to tell you it's going to break down,'' said Brad Colman of the meteorology department at the Massachussetts Institute of Technology. Analyzing Jan. 12 weather data, Mr. Colman said all indications point to a weather ''block'' in which the jet stream - a powerful core of winds sweeping generally in a west to east pattern around the Northern Hemisphere - does not fluctuate from its present state, continuing to deliver the same bitter cold conditions.
Colman's theory is not unfounded, says Robert Derouin, deputy chief of the forecast division of the National Meteorological Center in Washington.
''When you have a blocking in the Western part, it can persist for weeks at a time'' as it has in Europe, he says.
Mr. Derouin adds, ''Certainly this period will go down in history'' as one of the worst cold snaps in the US, especially because unusually strong winds have swept the record lows to such a widespread area.
For several days before the bitter cold arrived, Colman and Derouin agree, the jet stream was moving in a straight line across the US, separating warmer air to the south from cold air in the north. This dammed up a mass of cold air over Alaska that burst down onto the continental US when an arm of the jet stream buckled into a ridge over the Pacific Northwest. That is the pattern the two scientists expect to ''block'' - continuing to funnel cold air into the central and Eastern sections of the country.
As with most other types of extreme conditions, the bitter weather brought hardships but also examples of cooperation and even exaggeration:
* Chicago, perhaps the coldest spot on the national map, hit a record -26 F. at 9 a.m. Jan 10. With winds figured in, the chill factor dipped to -81 F.
Says Salvation Army spokesman Don Payton, ''We had the biggest weekend operation in our history.'' Volunteers helped Chicago firemen battle eight major blazes over the weekend, supplying them with dozens of doughnuts and some 1,200 meals.
The Salvation Army's three local shelters are ''bursting at the seams - just from people coming in off the streets,'' says Mr. Payton. They asked the city, now coordinating emergency efforts, for more cots.
The cold brought Midwest agricultural areas to a standstill, but, says Col. Ernest A. Miller, national public affairs director of the Salvation Army: ''Farmers do a lot to help each other. The whole idea of American voluntarism grew out of the Midwest.''
* Citrus-growers in Florida were reporting significant damage, despite efforts to stave off frost with smudge pots and even downdrafts from hovering helicopters.
Officials said the damage could exceed the devastating 1981 freeze, which destroyed $232 million in citrus, vegetable, and nursery crops in five counties and left 19,000 migrant farm workers and other people unemployed.
Trees were especially susceptible to freezing conditions, said a spokesman for Florida Citrus Mutual in Lakeland, because they still were not fully recovered from the 1981 freeze. And some spring-type weather last month brought early blooms to many citrus trees. The spokesman said 85 percent of the 1981-82 orange crop and 62 percent of the grapefruit crop have yet to be harvested.
The spokesman said citrus industry officials could not estimate the exact damage for several days and were unsure its impact.
But the strawberry crop of central Florida may have been spared, says Helen Parke of Plant City, wife of one of the area's largest producers. With the harvest due later this month, growers sprayed their plants as the cold weather moved in and the ice-encrusted berries and blossoms have not melted yet.
Still, says Mrs. Parke, damage is not expected to be as extensive as in the 1962 freeze.
Despite its agricultural worries, ''Florida was really lucky - they only got slop-over cold air'' and none of the high-powered cold that could have reached that far south, said one meteorologist.
* In New York, where city officials were besieged by as many as 325 calls an hour from heatless tenants at the peak of the cold spell, the ''heat fleet'' went into high gear.
Inspectors from the Housing and Preservation and Development Department are empowered to call for emergency fuel deliveries and boiler repairs - and bill landlords for them. They also may take legal action against landlords who fail to heat their buildings properly. Said one grateful tenant, ''These guys are cold-weather Supermen.''
* In Buffalo, where police officers tied stranded motorists together at the waist to lead them to safety from a snowbound expressway, one relief worker nonetheless insisted: ''I think the whole thing was blown out of proportion. Everybody tried to compare it to the big blizzard (1978), but it really wasn't that bad. It cleared up quickly.''
Meanwhile, say meteorologists Colman and Derouin, there may be slight relief from the cold as a Texas storm moves across the South and into New England bringing snow and slightly warmer temperatures at midweek. But they expect that storm to suck more bitter wind and cold behind it.