Newsprint has become scarce throughout the United States, forcing newspaper publishing companies to scramble for adequate supplies to fill their presses during the normally heavy fourth-quarter advertising period.

Strikes earlier this year at newsprint manufacturers, coupled with production difficulties in some instances, have caused a sharp reduction in newsprint inventories at virturally every major newspaper.

Although newspaper executives predicted a severe squeeze in coming weeks, as holiday season advertising begins to expand, they said they do not expect any curtailment of news content or advertising volume as a result of the newsprint situation.

Many publishers have taken steps to reduce excess newsprint consumption in their own press rooms, however. And the Gannet Co., with 80 daily newspapers the largest U.S. chain in terms of number of markets and papers, has told its regional divisions to cut back by as much as 7 percent on newsprint consumption that was budgeted when the year began.

Several newspapers, including The Washington Post, have been using newsprint imported from Europe. Also in the Washington area, Army Times Publishing Co. has started to turn away from its presses some business -- outside printing contracts -- in order to conserve paper for the firm's military newspapers and the five Journal newspapers, which are published twice weekly and have a circulation of 120,000 in the D.C. suburbs.

Barry McCarthy, a spokesman for the New York Times Co., said that on the basis of current newsprint inventories and "shipments fully expected . . . we will get through the fourth quarter, but with not much excess, if any."

The company's flagship in New York, The Times, is one of the fattest newspapers in the world and is expected to consume 300,000 tons of newsprint this year. But about 86 percent of newsprint for The Times comes from paper companies in Canada that are partly owned by the Times Co., which helps guarantee delivery under contracts.

"The newsprint situation has never been tighter in my experience," added McCarthy, who said the firm's newspapers in the South faced a more serious squeeze. The smaller papers use about 17,000 tons of newsprint a year.

One factor in increased need for newsprint for The Times is a substantial increase in advertising volume. August ad lines were up about 6 percent from the comparable period in 1977, with the 1978 period excluded because of the impact of a strike.

Like other newspaper firms, the Times Co. also has been hit -- earlier than expected -- by an increase in newsprint prices to $375 a ton from $345 a ton, effective Nov. 1 in the case of the Times but earlier this week for some other publishers.

At Gannett headquarters in Rochester, N.Y., Senior Vice President Douglas McCorkindale said his firm had an inventory on hand of slightly more than 30 days, compared with a desired supply of about 45 days. Gannett papers are expected to use 430,000 tons of newsprint this year, and 500,000 tons are budgeted for 1980, when no serious supply problem is anticipated.

"Tight. . .tight. . .tight," was the assessment of the newsprint situation by Washington Post Co. President Mark Meagher, who said inventories had been low all year before recent supply cutbacks exacerbated the situation. "We have not had to miss anything. . .and expect no cutbacks," although one supplier is 23 days behind schedule in making newsprint deliveries and does not expect to make up for the loss by year's end, Meagher added. The Post normally had about 20,000 tons on hand but the inventory currently is under 10,000 tons.

Overall, the Post Co. uses about 175,000 tons of newsprint a year -- 160,000 tons for The Washington Post and the balance for dailies in Trenton, N.J., and Everett, Wash. "We have to manage well; there's no three-week to six-week buffer," he added. Meagher said the Post Co. and many other publishers are searching for available newsprint in this country and abroad.

Dow Jones & Co., publisher of The Wall Street Journal and other daily papers, has a supply on hand of about six weeks compared with a normal inventory of up to three months, said George Flynn, senior vice president. Dow Jones uses about 150,000 tons a year.

According to industry officials, the tightest squeeze is hitting newspapers in New England. International Paper Co. recently announced a 7 percent cutback on an annual basis of newsprint supplied under contract to its customers -- with all of the reduction taking place in the fourth quarter. Officials said this could mean a shortage of up to 35 percent in newsprint required at some papers for the next three months. IP cited equipment problems for the delivery cutbacks.

Newsprint consumption has been rising during several mill strikes, with no corresponding boost in plant capacity. With new production facilities being built, the newsprint situation is expected to ease by next year.

In addition, the recession is expected to cut into advertising volume in the near future, according to John Morton, of the Wall Street firm of John Muir & Co. He said yesterday that ad lines in papers had remained stronger than expected through recent months but should slip in the current quarter.