Gov. John N. Dalton, bowing to pressure from Virginia business interests, reversed his administration's position today and vetoed a bill that would have put new restrictions on development in the state's vast ecologically fragile wetlands areas.

Dalton ignored pleas from state conservationist groups as well as those of his own state Council on the Environment and Secretary of Commerce and Resources Maurice B. Rowe, whose staff drew up the original bill. Instead, he heeded political ally state Sen. Herbert H. Bateman (R-Newport News) and lobbyists from the state Chamber of Commerce, Manufacturers Association and Association of Marine Industries, who met with Dalton last Monday to argue that the bill last Monday to argue that the bill could hurt the state's economic growth.

Later tonight -- the deadline for the governor's approval of bills from the 1980 legislature, which adjourned 30 days ago -- Dalton surprised many political observers by signing into law a bill repealing the state's 4 percent sales tax on home heating fuels effective in July 1982.

Critics contended the net effect of Dalton's veto will be to leave protection of the huge area in the hands of the federal government, which the conservative Republican governor usually derides.

"It's a real setback for Virginia's taking care of its own natural resources in a responsible fashion," said Del. George W. Grayson (D-Williamsburg), one of the bill's chief backers. He described it as "the most important piece of environmental legislation to pass the General Assembly in eight years" since the original state wetlands bill was enacted.

Other critics argued that the bill itself would not have significantly deterred development in the wetlands and said that business groups opposed its signing in order to stop conservationists from gaining a political foothold in a state that has traditionally emphasized growth over environmental considerations.

"They wanted it vetoed just on principle," said P.K. Pettus, lobbyist for the Conversation Council of Virginia who helped steer the bill through the legislature. "They don't want conservationists to claim a victory."

The bill would have brought Virginia's estimated 75,000 to 100,000 acres of nonvegetated wetlands under the same state protections that presently exist for vegetated areas. By definition, "nonvegetated wetlands" refers to land covered by water during high tide but dry during low tide.

Conservationists estimate that about two-thirds of the state's fin and shellfish spend part of their life cycle in these areas, most of which are in Tidewater Virginia but extend as far north as Fairfax County and Alexandria.

At present, building permits for nonvegetated areas must be approved by the U.S. Army Corps of Engineers which by practice asks for reviews from the Environmental Protection Agency and at least two federal wildlife agencies. Critics say the process is cumbersome an dunnecessary. Under the proposed law, approval instead would have been granted by local wetlands boards appointed by local governing bodies.

But the bill ran into a snag over a section proposed by marina owners that would have directed the local boards to approve construction by commercial and industrial developers pro vided fish life and the landscape "are not unreasonably affected." Bill sponsor Bateman had agreed to the section, which was not in the version drafted by Rowe's office.

Conservationists had argued that the section would tilt the present wetlands law in favor of developers and succeeded in stripping it from the bill. They cited a memo from Assistant Virginia Attorney General Frederick S. Fisher, who argued the section "would seriously weaken the existing wetlands law, would tend to invite litigation and would reduce the flexibility of the act."

Dalton administration officials, who had backed the new section, had said after getting Fisher's memo that they would support the bill with or without the language.

But at Bateman's urging, Dalton later exercised his power to request an amendment to the already-passed bill. The amendment, which would have restored the development section, passed the Senate by one vote but was crushed by 71 to 12 in the House on the last night of the session,

In a meeting last week, Dalton told conservation lobbyist Pettus he was "embarrassed" about the veto he was planning. "He said to me three times that this is the first time I've ever had to veto an administration bill," said Pettus.

Dalton press secretary Paul G. Edwards said today, "Without the Bateman language, it was no an administration bill. He [Dalton] feels three aren't suitable safeguards for private owners and developers."

Pettus said that even though the bill was vetoed, she considered it a major victory for her group. "The fact that we've got the governor and a senior Republican senator forced to veto their own bill shows we have some muscle," she said.

Dalton's veto effectively kills the wetlands bill. Under the state constitution, the Democrat-dominated General Assembly cannot reconvene until next January to reconsider the vetoed bill.

Many observers had expected the conservative governor to veto the home heating tax repeal bill, which will cost the state an estimated $23 million per year in revenues. The repeal will mean a savings of $20 annually to homeowner spending $500 each winter on fuel oil, propane, coal and firewood, but not affect those who heat their homes with natural gas or electricity.