The Food and Drug Administration has stepped up actions against misleading advertising by drug companies, but has scrapped a mandatory program that would have informed consumers directly about the side effects of a number of prescription products.

The agency accused a major pharmaceutical manufacturer, Pfizer Inc., of conducting a "false and misleading" advertising campaign to promote a new heart drug called nifedipine for the treatment of angina, or chest pain. Pfizer denied the charges.

In a warning letter calling for immediate corrective actions, the federal regulatory agency charged that promotional material prepared by Pfizer this year for physicians "increases the risk of serious adverse reactions to patients by omitting and misrepresenting important warning and precautionary information."

The strongly worded warning comes in the wake of other recent government criticisms of the promotion of anti-arthritis medications, including Oraflex, a controversial drug that recently was withdrawn from the market here by the manufacturer, Eli Lilly & Co..

Dr. Lloyd Millstein, acting director of the FDA's division of drug advertising and labeling, said yesterday that the increase in warning letters to drug companies was not a new effort, but simply a response to "a general increase in the level of advertising and greater competition in the marketplace. . . . Drug companies are beginning to make statements outside of good advertising."

In the case of nifedipine, which is being marketed as Procardia, Millstein said that the FDA was concerned about overpromoting the drug for all types of angina and "comparison to other products and stating it was different or better because it did not have the same side effects."

Procardia went on the market earlier this year as the first oral form of a new class of drugs known as calcium channel blockers, which can reduce the coronary artery spasms that are one cause of angina. It followed the introduction last year of an injectable calcium blocker called verapamil, which is manufactured by Knoll Pharmaceutical Co. as Isoptin and by G.D. Searle & Co. as Calan.

Procardia has captured the lion's share of the market, in part because of its aggressive advertising campaign, says one FDA source. A Pfizer spokesman said yesterday that the company would meet again with the FDA but added that "we believe the statements made in our advertising pieces were truthful and not false or misleading."

The FDA letter said that Procardia should not be promoted as a "first-line therapy in the treatment of angina patients," but should be prescribed under limitations outlined in the labeling. It said attempts to compare the drug with a competitor, verapamil, were "selective and distorted," neglecting to mention, for example, that a potentially-life-threatening drop in blood pressure can be associated with either drug if recipients are not monitored carefully.

Claims of Procardia's "superiority" over other drugs are based on "untruths, partial truths and omitted information," the FDA said. It asked the company to cancel current advertising and send a corrective letter to all physicians that already have been contacted.

The FDA also announced a final order yesterday to cancel a Carter administration proposal to inform consumers directly about a number of drugs. The so-called "mandatory patient package insert" pilot program involving 10 drugs was dropped in favor of alternative voluntary efforts.