The tobacco industry has begun an aggressive campaign-donation drive, pouring more than $1.5 million into national Republican Party treasuries in the first half of 1995, five times as much as in the period last year.

The surge in donations comes when the industry is facing the most serious threats from Washington in its history.

The industry’s chief worry comes from the Food and Drug Administration, which is moving to have nicotine declared an addictive drug, a fundamental change in the government’s approach to tobacco. The government now limits cigarette advertisements and requires warnings on packages, but under the FDA proposal the agency would be able to regulate the product itself.

The Philip Morris Cos. alone gave $729,749 to Republican funds from January to July, a sevenfold increase from the $99,000 given to Republicans and Democrats combined during the period last year.

Philip Morris and two other companies, RJR Nabisco, which gave $286,450, and Brown & Williamson, which gave $260,000, accounted for most of the industry’s gifts.

“What you have is the tobacco lobby with their backs against the wall,” said Ann McBride, president of Common Cause, the group that compiled the figures. “It is the singlemost-aggressive campaign to use money to buy influence in the opening months of a Congress.”