The proposed merger between the Hospital Corp. of America and American Hospital Supply Corp. -- the biggest companies in their respective fields -- is not expected to hurt competition in the hospital or medical supply industries, according to antitrust experts and financial analysts.

The merged company, which would have annual sales of almost $8 billion, will continue to face large numbers of healthy competitors in both industries, and will gain little economic advantage over them, according to antitrust experts.

The merger may help HCA control its supply costs in response to pressure from the government and corporate employers. But analysts say cutting costs will not put more patients in hospital beds. This, they say, is the major challenge facing the hospital industry with declining occupancy rates and increasing competition from alternative health care delivery systems.

The merger "does nothing to fill beds," said Seth Shaw, an analyst with Shearson Lehman Bros. Inc. "It won't affect competition at all."

After the merger, "there will be the same number of hospital companies and the same number of suppliers," said Joe Sims, an antitrust expert with the law firm Jones, Day, Reavis & Pogue. "It's hard to see how it will affect competition in either market."

Mergers of this size routinely are reviewed by the Federal Trade Commission or the Justice Department for possible anticompetitive effects. The two agencies rarely challenge "vertical mergers," which combine firms operating in different markets, at different stages of a production and delivery process.

"There is a general recognition in the economic literature of the efficiencies of vertical relations," said Charles F. Rule, acting director of the Justice Department's antitrust division. "By enabling different links in the chain to better coordinate activities, companies can deliver products to consumers at lower costs."

Theoretically, a vertical merger can hurt competition if it raises other firms' costs by limiting their access to an important resource, or if it limits the entry of new firms into the markets.

The HCA-AHS merger will not hurt competition in the hospital industry, analysts say, and HCA will not be able to control the prices or availability of medical supplies to its rivals. Nor will it be able to limit the entry of new competitors into the two markets, analysts said.

"Neither company significantly controls the markets it competes in," said David J. Lothson, an analyst with Paine Webber Inc. "The hospital industry is highly fragmented."

HCA, the largest for-profit hospital company in the country, owns or manages about 5 percent of the hospitals and about 5 percent of the hospital beds (55,000 of 1.2 million beds) in the nation.

The four largest investor-owned, for-profit hospital companies, together own about 10 percent of the nation's hospital beds. About two-thirds of the remaining market operate under religious or community charter, and the rest are government-run.

AHS, the nation's largest medical supply company, is both a distributor and manufacturer of items ranging from band-aids to surgical instruments, from bedpans to chemical reagents, controlling about 28 percent of the domestic market.

AHS is the only medical supply company with a national distribution system, but faces regional and local competitors including Bergen Brunswig Corp. and Whittaker Corp. It also competes with more than 500 manufacturers of medical and laboratory supplies, including giants like Abbott Laboratories, Baxter Travenol Laboratories and Johnson & Johnson.

To be sure, AHS is "the dominant factor in hospital supply," with 1984 profits of $238 million on sales of $3.5 billion, said Joel D. Liffman, an analyst with Drexel Burnham Lambert Inc. AHS "sets the competitive pace in industry pricing and service.

But because of its size, it could not survive as an exclusive supplier to HCA.

AHS expects its sales to HCA to amount to $125 million in 1985. HCA spends about $800 million a year on supplies, so AHS could fill all its needs and still sell $2.7 billion worth of goods to other hospitals -- including HCA's competitors.

"Economically, AHS sure better have other customers," Liffman said. "They have to keep selling to others."

Indeed the merger could hurt AHS if the other major hospital chains decide not to do business with their rival's new subsidiary. That could touch off a "scramble" by other suppliers for those sales, forcing down prices, Liffman said. "There are other sources of supply at competitive prices."

Other analysts doubt that HCA's competitors will cut off AHS. They are all under pressure to cut costs and will buy from the supplier offering the best price, Shaw said.

HCA is following that logic. Intravenous solutions are one of AHS' big products, but HCA recently signed a three-year, $40 million a year contract to buy the product from Baxter Travenol, Liffman said.

The merger of the two companies is "just diversification, not integration," Shaw said.

AHS was the target of a private antitrust suit filed in 1979 by four competitors, challenging a contract between AHS and the Voluntary Hospitals of America that gave VHA volume discounts in return for purchasing large amounts of certain products.

A federal appeals court unanimously dismissed the case, calling the agreement legal, competitive and "of significant benefit to hospital customers," said an AHS spokeswoman.

Although the merger may not give the two companies a competitive edge in their respective markets, it does create a financial base for expansion into new markets. The combined company can take on more than $1 billion in additional debt, according to some estimates.

"The competitive advantage of the merger is the creation of a national infrastructure for the delivery of health care," Liffman said. The merger alone "does not address the fundamental problem facing both industries of declining hospital utilization."