(FORTUNE Magazine) – -- Suppose the Republicans don't pull it together. Suppose President Bush, hamstrung by a sluggish economy, loses in the fall. While the stock market might heave and sway under a new Administration, some stocks will surely flourish. Thanks to the highly detailed Democratic platform, and Clinton's exhaustive speeches, investors already can get a fix on shares most likely to shoot up if Dems win. Here are the most likely beneficiaries:

-- Infrastructure. At the center of Clinton's economic proposal is the Rebuild America Fund, which calls for the federal government to spend an additional $20 billion annually for the next four years on roads, bridges, tunnels, and sewers. Thomas Gallagher, political analyst for Shearson Lehman Brothers in Washington, D.C., calls Clinton's proposal a ''pretty big reallocation of resources.'' Says he: ''If only a little of it trickles down, a lot of companies will get wet in all aspects of the business.'' The biggest beneficiaries would be companies such as Granite Construction, Greiner Engineering, and Kasler, which specialize in the design and construction of roads, bridges, and tunnels. Granite trades on Nasdaq, while Greiner and Kasler are on the Big Board. The companies are quite small, but they are pure plays. Granite is the largest, with 1991 revenues of $564 million. John Simon, an analyst at Seidler Amdec in Los Angeles, thinks their small size and concentrated business lines make them the biggest potential gainers if construction spending picks up. Shearson's Gallagher points out that demand for steel should rise too. Birmingham Steel, the largest producer of reinforcement bars for concrete highways, should prosper. Thomas Van Leeuwen, Shearson's steel analyst, expects that the company will report earnings of $1.65 per share for the year ended in June, and $2 in 1993.

-- Environment. Hazardous-waste-disposal companies may be the best bet. Michael Reckmeyer, environmental analyst at Kemper Financial Services, thinks the Democrats would speed enforcement of existing EPA regulations by closing loopholes nudged open by the deregulatory Bush team. They might also regulate more categories of waste, such as sludge. The most obvious beneficiaries, according to Reckmeyer, would be Chemical Waste Management, Safety-Kleen, and Rollins Environmental Services. Companies that help utilities and manufacturers comply with the Clean Air Act are already prospering under the Bush Administration. A Clinton victory would only make the outlook brighter, says Paul Knight, pollution control analyst at County NatWest. His top picks are TRC Cos., Thermo Instrument Systems, and Environmental Elements. These companies are already growing at better than 20% annually.

-- Health care. Clinton's platform calls for ''universal'' health coverage and advocates a managed-care network. Says Margo Vignola, a health services analyst at Salomon Brothers: ''The HMOs are well positioned under a Democratic Administration.'' Her favorites are United HealthCare and U.S. Healthcare.

-- Training. Clinton would require employers to spend 1.5% of payroll for education and training. This money would flow to companies that sell such services, like National Education, the country's largest technical training firm. ''Clinton's plan would be absolutely fantastic for the company,'' says Andrew Knuth at Westport Asset Management in Connecticut. He is increasing his already sizable holding and expects the company to earn about 40 cents per share this year and 65 cents in 1993. The stock recently traded at $7.50 per share.