WASHINGTON, May 22 -- With just two days to go before Congress decides whether to upgrade economic ties with China, corporate supporters opened a $1 million advertising blitz today and labor opponents stormed Capitol Hill as both camps struggled to recruit a handful of undecided lawmakers who hold the key to victory or defeat.

The Clinton administration, which considers the vote on permanent normal trade relations its top remaining legislative priority, now expects a narrow win. But administration officials say they still need six to eight undecided Democrats and a similar number of uncommitted Republicans to vote their way if the measure is to pass the House, where a vote is scheduled for Wednesday.

Business groups have filled the airwaves as their $8 million advertising campaign -- corporate America's costliest legislative campaign ever -- ends this week. The United States Chamber of Commerce assigned a lobbyist to each undecided lawmaker on its target list, while President Clinton has set aside several hours each day this week for telephone calls and face-to-face meetings with wavering Democrats, White House officials said.

Labor unions, insisting that they still have a chance to defeat the measure that they call a threat to America's working class, are turning up the heat on a small group of Democrats who need union support in the fall elections. Union officials planned a Capitol Hill vigil for tomorrow and are flying in shop-floor leaders to apply pressure to lawmakers in the hours before the vote.

Last-minute horse-trading with several undecided members also continued today. Two Texas Congressmen wanted help with a gas pipeline, while a Minnesota lawmaker urged the Clinton administration to protect iron ore workers, Congressional aides and administration officials said.

The final lobbying flurry underscored how the China trade vote has become a test of political strength for both business and labor. Business executives boasted that they had run their most effective vote-getting effort in recent years by taking a page from labor's political playbook, organizing grass-roots, home-district lobbying efforts as well as national and regional advertising.

"We are sending so many people at these members that they can go home each night and tell their children they're famous," said Thomas Donohue, president of the chamber.

Union officials said they had mobilized members nationwide and honed their political message not just on trade, but also for the fall elections, when they hope to make Democrats the majority party in Congress. John Sweeney, president of the A.F.L-C.I.O; James Hoffa, president of the Teamsters; and George Becker, president of the United Steelworkers of America, planned to spend the remaining two days visiting a handful of Democrats and Republicans whom union officials feel might still vote no on the trade issue.

Supporters and opponents largely agreed on the vote count in the House, where the matter is likely to be decided. White House officials said they had about 65 Democratic votes and wanted 7 more; Republicans had 145 committed yes votes and hoped to recruit another 10. If both achieve their goals, that would give a comfortable cushion over the 218 needed, but White House officials acknowledged that they had to fight for every new supporter. Approval by the Senate appears more certain.

President Clinton has argued that Congress should grant China permanent trade status for both economic and national security reasons. Ending the annual Congressional review of China's trading rights would guarantee American companies the full benefits of China's entry into the World Trade Organization, the administration says. A negative vote, it says, could lead to a diplomatic standoff with Beijing and instability in Asia.

Opponents, led by labor unions as well as environmental, human rights and consumer groups, argue that China does not deserve higher trade status because it does not adhere to Western labor or environmental standards. Unions also say they fear that more open trade with China would encourage companies to move good industrial jobs there.

One of the truly undecided members of Congress being cajoled and warned by both camps is Eva M. Clayton, a North Carolina Democrat. Because her district has a heavily agricultural base, the Clinton administration and farm groups have pressured her to help North Carolina farms export more to China. But teachers and communications workers in the district have made her a prime target as well, and Mr. Sweeney has called on her repeatedly as the vote approaches, union officials said.

"I think her fondest wish is to be left alone," one lobbyist said today.

On many other trade issues in recent years, unions have proven more politically effective than big business, defeating many of the administration's trade goals including its efforts to win "fast track" trade negotiating authority.

But business groups, including the Business Roundtable and the chamber, determined late last year that the China vote was too important to lose.

The 200-member Business Roundtable took the lead in advertising in 27 Congressional districts, including a barrage of ads during the Easter Congressional recess and another blitz during the last week.

Some individual corporations have also run ads supporting upgraded trade relations. Motorola has been among the most active, spending more than $1 million on newspaper and television ads during news shows.

The Illinois-based telecommunication company has invested more than $1 billion in China and fears that European competitors will benefit at its expense if Congress denies China the new trading rights.

Looking to neutralize labor's vaunted local organization on the ground, where it can deliver votes for members in tight races, business groups have also mobilized employees to write letters and visit Congressmen, as labor unions have done for years. Intel alone had employees write 5,000 such letters, company officials said.

"Unions have been superbly successful on trade issues and we have really learned from them," said Robert N.

Burt, chairman and chief executive of FMC Corporation, a chemicals and machinery manufacturer, and head of the Business Roundtable.

Mr. Burt said businesses had also become more savvy about how to leverage their soft-money donations to persuade members of Congress to support important business measures, including the China trade bill.

Financially, the business lobbying effort has swamped labor. But labor and its supporters, including the Family Research Council, a family values association, have spent about $2 million on ads opposing the trade bill. Union officials said it is easily their largest financial commitment to a single legislative issue.

Union officials have also bluntly warned lawmakers that local support for their re-election campaign hinges on voting no on the trade matter, members of Congress said. But some members said they believed that labor's goal of helping Democrats win back the House is ultimately more important than punishing members for voting in favor of the bill.