YOSEMITE NATIONAL PARK, CALIF. — YOSEMITE NATIONAL PARK, Calif. -- Environmentalists hav long complained about commercialism and overcrowding in this jewel of the National Park system. But the truth may be worse: Soil and water under the park are polluted with toxic chemicals that have leaked from underground fuel tanks for decades. The contamination has become a major issue in the bidding to buy the company that provides hotel, restaurant and other visitor services in the 102-year-old park. Citing the possible financial liability for cleaning up the company's pollution, one major potential bidder dropped out of the race for the coveted 15-year contract this month. The dropout, Host International, a subsidiary of the Marriott Corp., said the liability could eat up or even exceed the profits. The pollution, and other financial uncertainties, raises the question of whether there will be any suitable entrants by the Nov. 16 deadline set by the National Park Service for bids on what at $87 million is by far the largest concession contract in the national park system. The competition for the Yosemite contract has been widely watched as a national model for redefining the role of private operations in the parks. Ultimately, the park service goal is reduced commercialization in the parks and higher fees to the government. Workers are cleaning up 38 sites polluted with toxic chemicals from heating fuel, gasoline, diesel fuel and solvents like paint thinner. They are still digging up and testing the areas around some 50 storage tanks that could be leaking. The work is being paid for by the company that has operated the the park's concessions for years, the Yosemite Park and Curry Co., a telephone company, Pacific Bell, and the park service. State and park service officials say the pollution poses no direct threat to the park's 3.5 million annual visitors. They say the chemicals are far above the 300-foot-deep wells used for drinking water and are in areas either paved over or fenced off from public use. Nor is the contamination any more serious than that routinely found today in most cities near gas stations and industrial areas. But it will come as a surprise to park visitors seeking refuge from urban ills in this land of soaring granite walls, bighorn sheep, black bears and giant sequoias. Visitors have already been jarred this summer, when, for the first time ever, the park service banned daytime campfires in Yosemite Valley because of growing air pollution in the narrow mile-wide valley. The park service has already taken some of the luster off the contract by asking the new concessionaire to reduce lodgings by 15 percent, move its headquarters and much employee housing out of the park and pay the government at least 5 percent of gross receipts into a capital improvement fund, up from 0.75 percent now paid by the Yosemite Park and Curry Co. under the 30-year-contract expiring next year. Under the new contract, all the fees would be earmarked for Yosemite improvements, instead of going into a general fund. In addition, the new owner will have to spend $29 million on new park improvements, build housing for employees outside the park, pay for an as-yet-undesigned new transportation system for visitors and staff members, take on such new responsibilities as snow plowing and buy out the equity -- known as "possessory" interest -- that Curry has accrued by building and improving the hotels and other park structures over the years. The Curry Co. is a subsidiary of MCA Inc., the Los Angeles-based entertainment conglomerate that was sold last year to the Matsushita Electric Industrial Co. of Japan. As part of the Park Service's contract with MCA, the new owner must both pay MCA for that possessory interest -- valued at $61.5 million -- and take on the new responsibilities to renew the Curry contract. Curry's earnings before taxes last year were $9 million on gross revenues of $87 million. The debt burden and new responsibilities plus possibly millions for additional cleanup of underground pollution will weigh heavy in the balance as companies decide whether to bid for the contract. "We need someone who can pay us the most money fastest and operate it effectively," said Stephen G. Crabtree, chief of the office of concessions management at the park service's regional headquarters in San Francisco. Seizing on public resentment over Japanese ownership of American companies, Interior Secretary Manuel Lujan Jr. browbeat MCA into waiving its preferential right to renew the Yosemite contract when it expires on Sept. 30, 1993 and to sell Curry to an American concern. MCA also agreed to finance the sale of Curry, valued at $61.5 million, with a 15-year-note at 8.5 percent annual interest. None of the potential bidders has decided yet whether the purchase of Curry and taking on the contract is a good deal. They include two concessionaires with long experience in other parks, two hotel and resort operators, three food-service companies, and a group of former Disney employees. What's more, there are two environmentally oriented groups dedicated to taking over the concession to reduce commercialization by accepting reduced profits. Each must be able to raise at least $12 million. Host International dropped out, said Roger E. Mann, senior director of business development, because the terms were not attractive, particularly considering the pollution. "Our environmental attorneys and engineers believe that remediation could cost millions of dollars every year for an indefinite period and that a precise amount will not be known until the remediation is complete," Mr. Mann wrote the park service in a letter withdrawing from the bidding. In an interview, he added that the cost "could be millions a year for the life of the contract." Host asked the park service to indemnify the concessionaire against future pollution liabilities, a suggestion rejected out of hand by Yosemite's superintendent, Michael V. Finley. "We are not going to do that," he said in an interview, adding that he thought most of the sites had been identified. "We've gone through the historical records and asked where there was a service station," he said. "If anything else is out there, the likelihood is real low." No fault has been laid at the feet of the current management of the Curry company, which has operated here since 1899 and is widely admired for its recycling and other conservation efforts. Most of the leakage has come from corroded underground tanks installed decades ago, as far back as 1920. Of the 38 polluted sites, 24 were from tanks owned by the Curry company, 10 by the National Park Service and four by Pacific Bell. Among the toxic chemicals that have been found are benzene, toluene, xylene and ethylbenzene.